diff --git a/Octokit.Tests/Clients/DeploymentStatusClientTests.cs b/Octokit.Tests/Clients/DeploymentStatusClientTests.cs
index f01cb8bf..e59b26af 100644
--- a/Octokit.Tests/Clients/DeploymentStatusClientTests.cs
+++ b/Octokit.Tests/Clients/DeploymentStatusClientTests.cs
@@ -14,21 +14,21 @@ public class DeploymentStatusClientTests
     public class TheGetAllMethod
     {
         [Fact]
-        public void EnsuresNonNullArguments()
+        public async Task EnsuresNonNullArguments()
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
-                
-            Assert.Throws<ArgumentNullException>(() => client.GetAll(null, "name", 1));
-            Assert.Throws<ArgumentNullException>(() => client.GetAll("owner", null, 1));
+
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll(null, "name", 1));
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll("owner", null, 1));
         }
 
         [Fact]
-        public void EnsuresNonEmptyArguments()
+        public async Task EnsuresNonEmptyArguments()
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
-                
-            Assert.Throws<ArgumentException>(() => client.GetAll("", "name", 1));
-            Assert.Throws<ArgumentException>(() => client.GetAll("owner", "", 1));
+
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("", "name", 1));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("owner", "", 1));
         }
 
         [Theory]
@@ -37,12 +37,12 @@ public class DeploymentStatusClientTests
         [InlineData("\t")]
         [InlineData("  ")]
         [InlineData("\n\r")]
-        public void EnsureNonWhitespaceArguments(string whitespace)
+        public async Task EnsureNonWhitespaceArguments(string whitespace)
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
-                
-            Assert.Throws<ArgumentException>(() => client.GetAll(whitespace, "name", 1));
-            Assert.Throws<ArgumentException>(() => client.GetAll("owner", whitespace, 1));
+
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll(whitespace, "name", 1));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("owner", whitespace, 1));
         }
 
         [Fact]
@@ -76,21 +76,21 @@ public class DeploymentStatusClientTests
         readonly NewDeploymentStatus newDeploymentStatus = new NewDeploymentStatus();
 
         [Fact]
-        public void EnsuresNonNullArguments()
+        public async Task EnsuresNonNullArguments()
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
-                
-            Assert.Throws<ArgumentNullException>(() => client.Create(null, "name", 1, newDeploymentStatus));
-            Assert.Throws<ArgumentNullException>(() => client.Create("owner", null, 1, newDeploymentStatus));
+
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, "name", 1, newDeploymentStatus));
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", null, 1, newDeploymentStatus));
         }
 
         [Fact]
-        public void EnsuresNonEmptyArguments()
+        public async Task EnsuresNonEmptyArguments()
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
                 
-            Assert.Throws<ArgumentException>(() => client.GetAll("", "name", 1));
-            Assert.Throws<ArgumentException>(() => client.GetAll("owner", "", 1));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("", "name", 1));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("owner", "", 1));
         }
 
         [Theory]
@@ -99,12 +99,12 @@ public class DeploymentStatusClientTests
         [InlineData("\t")]
         [InlineData("  ")]
         [InlineData("\n\r")]
-        public void EnsureNonWhitespaceArguments(string whitespace)
+        public async Task EnsureNonWhitespaceArguments(string whitespace)
         {
             var client = new DeploymentStatusClient(Substitute.For<IApiConnection>());
                 
-            Assert.Throws<ArgumentException>(() => client.Create(whitespace, "repo", 1, newDeploymentStatus));
-            Assert.Throws<ArgumentException>(() => client.Create("owner", whitespace, 1, newDeploymentStatus));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.Create(whitespace, "repo", 1, newDeploymentStatus));
+            await Assert.ThrowsAsync<ArgumentException>(() => client.Create("owner", whitespace, 1, newDeploymentStatus));
         }
 
         [Fact]
diff --git a/Octokit.Tests/Clients/FollowersClientTests.cs b/Octokit.Tests/Clients/FollowersClientTests.cs
index 3d2fddd2..3d7d3314 100644
--- a/Octokit.Tests/Clients/FollowersClientTests.cs
+++ b/Octokit.Tests/Clients/FollowersClientTests.cs
@@ -56,13 +56,13 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new FollowersClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAll(null));
-                Assert.Throws<ArgumentException>(() => client.GetAll(""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll(null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll(""));
             }
         }
 
@@ -94,13 +94,13 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new FollowersClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.GetFollowing(null));
-                Assert.Throws<ArgumentException>(() => client.GetFollowing(""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetFollowing(null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetFollowing(""));
             }
         }
 
diff --git a/Octokit.Tests/Clients/GistsClientTests.cs b/Octokit.Tests/Clients/GistsClientTests.cs
index 53c56a68..51a61865 100644
--- a/Octokit.Tests/Clients/GistsClientTests.cs
+++ b/Octokit.Tests/Clients/GistsClientTests.cs
@@ -163,7 +163,7 @@ public class GistsClientTests
             var connection = Substitute.For<IApiConnection>();
             var client = new GistsClient(connection);
 
-            Assert.Throws<ArgumentNullException>(() => client.Delete(null));
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete(null));
         }
     }
 
diff --git a/Octokit.Tests/Clients/IssuesClientTests.cs b/Octokit.Tests/Clients/IssuesClientTests.cs
index 8b5aa4f4..b50c0f6c 100644
--- a/Octokit.Tests/Clients/IssuesClientTests.cs
+++ b/Octokit.Tests/Clients/IssuesClientTests.cs
@@ -116,16 +116,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new IssuesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.GetForRepository(null, "name", new RepositoryIssueRequest()));
-                Assert.Throws<ArgumentException>(() => client.GetForRepository("", "name", new RepositoryIssueRequest()));
-                Assert.Throws<ArgumentNullException>(() => client.GetForRepository("owner", null, new RepositoryIssueRequest()));
-                Assert.Throws<ArgumentException>(() => client.GetForRepository("owner", "", new RepositoryIssueRequest()));
-                Assert.Throws<ArgumentNullException>(() => client.GetForRepository("owner", "name", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetForRepository(null, "name", new RepositoryIssueRequest()));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetForRepository("", "name", new RepositoryIssueRequest()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetForRepository("owner", null, new RepositoryIssueRequest()));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetForRepository("owner", "", new RepositoryIssueRequest()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetForRepository("owner", "name", null));
             }
         }
 
@@ -145,16 +145,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new IssuesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Create(null, "name", new NewIssue("title")));
-                Assert.Throws<ArgumentException>(() => client.Create("", "name", new NewIssue("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", null, new NewIssue("x")));
-                Assert.Throws<ArgumentException>(() => client.Create("owner", "", new NewIssue("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", "name", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, "name", new NewIssue("title")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", "name", new NewIssue("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", null, new NewIssue("x")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("owner", "", new NewIssue("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", "name", null));
             }
         }
 
@@ -174,16 +174,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new IssuesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Update(null, "name", 1, new IssueUpdate()));
-                Assert.Throws<ArgumentException>(() => client.Update("", "name", 1, new IssueUpdate()));
-                Assert.Throws<ArgumentNullException>(() => client.Update("owner", null, 1, new IssueUpdate()));
-                Assert.Throws<ArgumentException>(() => client.Update("owner", "", 1, new IssueUpdate()));
-                Assert.Throws<ArgumentNullException>(() => client.Update("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Update(null, "name", 1, new IssueUpdate()));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Update("", "name", 1, new IssueUpdate()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Update("owner", null, 1, new IssueUpdate()));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Update("owner", "", 1, new IssueUpdate()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Update("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/MilestonesClientTests.cs b/Octokit.Tests/Clients/MilestonesClientTests.cs
index 7c468939..a2fc65bd 100644
--- a/Octokit.Tests/Clients/MilestonesClientTests.cs
+++ b/Octokit.Tests/Clients/MilestonesClientTests.cs
@@ -81,16 +81,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new MilestonesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Create(null, "name", new NewMilestone("title")));
-                Assert.Throws<ArgumentException>(() => client.Create("", "name", new NewMilestone("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", null, new NewMilestone("x")));
-                Assert.Throws<ArgumentException>(() => client.Create("owner", "", new NewMilestone("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", "name", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, "name", new NewMilestone("title")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", "name", new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", null, new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("owner", "", new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", "name", null));
             }
         }
 
@@ -110,16 +110,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new MilestonesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Create(null, "name", new NewMilestone("title")));
-                Assert.Throws<ArgumentException>(() => client.Create("", "name", new NewMilestone("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", null, new NewMilestone("x")));
-                Assert.Throws<ArgumentException>(() => client.Create("owner", "", new NewMilestone("x")));
-                Assert.Throws<ArgumentNullException>(() => client.Create("owner", "name", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, "name", new NewMilestone("title")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", "name", new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", null, new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("owner", "", new NewMilestone("x")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", "name", null));
             }
         }
 
@@ -137,15 +137,15 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArgumentsNotNull()
+            public async Task EnsuresArgumentsNotNull()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new MilestonesClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Delete(null, "name", 42));
-                Assert.Throws<ArgumentException>(() => client.Delete("", "name", 42));
-                Assert.Throws<ArgumentNullException>(() => client.Delete("owner", null, 42));
-                Assert.Throws<ArgumentException>(() => client.Delete("owner", "", 42));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete(null, "name", 42));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("", "name", 42));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete("owner", null, 42));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("owner", "", 42));
             }
         }
 
diff --git a/Octokit.Tests/Clients/OrganizationMembersClientTests.cs b/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
index c3f17b18..7ac2bfde 100644
--- a/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
+++ b/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
@@ -41,12 +41,12 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var orgMembers = new OrganizationMembersClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => orgMembers.GetAll(null));
-                Assert.Throws<ArgumentException>(() => orgMembers.GetAll(""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => orgMembers.GetAll(null));
+                await Assert.ThrowsAsync<ArgumentException>(() => orgMembers.GetAll(""));
             }
         }
 
@@ -64,12 +64,12 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var orgMembers = new OrganizationMembersClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => orgMembers.GetPublic(null));
-                Assert.Throws<ArgumentException>(() => orgMembers.GetPublic(""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => orgMembers.GetPublic(null));
+                await Assert.ThrowsAsync<ArgumentException>(() => orgMembers.GetPublic(""));
             }
         }
 
diff --git a/Octokit.Tests/Clients/OrganizationsClientTests.cs b/Octokit.Tests/Clients/OrganizationsClientTests.cs
index f7845b9e..86a617cb 100644
--- a/Octokit.Tests/Clients/OrganizationsClientTests.cs
+++ b/Octokit.Tests/Clients/OrganizationsClientTests.cs
@@ -35,11 +35,11 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var orgs = new OrganizationsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => orgs.Get(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => orgs.Get(null));
             }
         }
 
@@ -57,11 +57,11 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var orgs = new OrganizationsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => orgs.GetAll(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => orgs.GetAll(null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/ReleasesClientTests.cs b/Octokit.Tests/Clients/ReleasesClientTests.cs
index 3cea3340..63684bb7 100644
--- a/Octokit.Tests/Clients/ReleasesClientTests.cs
+++ b/Octokit.Tests/Clients/ReleasesClientTests.cs
@@ -49,14 +49,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var releasesClient = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => releasesClient.Get(null, "name", 1));
-                Assert.Throws<ArgumentException>(() => releasesClient.Get("", "name", 1));
-                Assert.Throws<ArgumentNullException>(() => releasesClient.Get("owner", null, 1));
-                Assert.Throws<ArgumentException>(() => releasesClient.Get("owner", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => releasesClient.Get(null, "name", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => releasesClient.Get("", "name", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => releasesClient.Get("owner", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => releasesClient.Get("owner", "", 1));
             }
         }
 
@@ -107,16 +107,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var releasesClient = new ReleasesClient(Substitute.For<IApiConnection>());
                 var releaseUpdate = new ReleaseUpdate { TagName = "tag" };
 
-                Assert.Throws<ArgumentNullException>(() => releasesClient.Edit(null, "name", 1, releaseUpdate));
-                Assert.Throws<ArgumentException>(() => releasesClient.Edit("", "name", 1, releaseUpdate));
-                Assert.Throws<ArgumentNullException>(() => releasesClient.Edit("owner", null, 1, releaseUpdate));
-                Assert.Throws<ArgumentException>(() => releasesClient.Edit("owner", "", 1, releaseUpdate));
-                Assert.Throws<ArgumentNullException>(() => releasesClient.Edit("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => releasesClient.Edit(null, "name", 1, releaseUpdate));
+                await Assert.ThrowsAsync<ArgumentException>(() => releasesClient.Edit("", "name", 1, releaseUpdate));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => releasesClient.Edit("owner", null, 1, releaseUpdate));
+                await Assert.ThrowsAsync<ArgumentException>(() => releasesClient.Edit("owner", "", 1, releaseUpdate));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => releasesClient.Edit("owner", "name", 1, null));
             }
         }
 
@@ -134,14 +134,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.Delete(null, "name", 1));
-                Assert.Throws<ArgumentException>(() => client.Delete("", "name", 1));
-                Assert.Throws<ArgumentNullException>(() => client.Delete("owner", null, 1));
-                Assert.Throws<ArgumentException>(() => client.Delete("owner", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete(null, "name", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("", "name", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete("owner", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("owner", "", 1));
             }
         }
 
@@ -161,14 +161,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAssets(null, "name", 1));
-                Assert.Throws<ArgumentException>(() => client.GetAssets("", "name", 1));
-                Assert.Throws<ArgumentNullException>(() => client.GetAssets("owner", null, 1));
-                Assert.Throws<ArgumentException>(() => client.GetAssets("owner", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAssets(null, "name", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAssets("", "name", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAssets("owner", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAssets("owner", "", 1));
             }
         }
 
@@ -235,14 +235,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAsset(null, "name", 1));
-                Assert.Throws<ArgumentException>(() => client.GetAsset("", "name", 1));
-                Assert.Throws<ArgumentNullException>(() => client.GetAsset("owner", null, 1));
-                Assert.Throws<ArgumentException>(() => client.GetAsset("owner", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAsset(null, "name", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAsset("", "name", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAsset("owner", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAsset("owner", "", 1));
             }
         }
 
@@ -262,15 +262,15 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.EditAsset(null, "name", 1, new ReleaseAssetUpdate("name")));
-                Assert.Throws<ArgumentException>(() => client.EditAsset("", "name", 1, new ReleaseAssetUpdate("name")));
-                Assert.Throws<ArgumentNullException>(() => client.EditAsset("owner", null, 1, new ReleaseAssetUpdate("name")));
-                Assert.Throws<ArgumentException>(() => client.EditAsset("owner", "", 1, new ReleaseAssetUpdate("name")));
-                Assert.Throws<ArgumentNullException>(() => client.EditAsset("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.EditAsset(null, "name", 1, new ReleaseAssetUpdate("name")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.EditAsset("", "name", 1, new ReleaseAssetUpdate("name")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.EditAsset("owner", null, 1, new ReleaseAssetUpdate("name")));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.EditAsset("owner", "", 1, new ReleaseAssetUpdate("name")));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.EditAsset("owner", "name", 1, null));
             }
         }
 
@@ -288,14 +288,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new ReleasesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.DeleteAsset(null, "name", 1));
-                Assert.Throws<ArgumentException>(() => client.DeleteAsset("", "name", 1));
-                Assert.Throws<ArgumentNullException>(() => client.DeleteAsset("owner", null, 1));
-                Assert.Throws<ArgumentException>(() => client.DeleteAsset("owner", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.DeleteAsset(null, "name", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.DeleteAsset("", "name", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.DeleteAsset("owner", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.DeleteAsset("owner", "", 1));
             }
         }
     }
diff --git a/Octokit.Tests/Clients/RepoCollaboratorsClientTests.cs b/Octokit.Tests/Clients/RepoCollaboratorsClientTests.cs
index 11eefa4d..92497cfa 100644
--- a/Octokit.Tests/Clients/RepoCollaboratorsClientTests.cs
+++ b/Octokit.Tests/Clients/RepoCollaboratorsClientTests.cs
@@ -37,14 +37,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepoCollaboratorsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAll(null,"test"));
-                Assert.Throws<ArgumentException>(() => client.GetAll("", "test"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAll("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAll("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll(null,"test"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("", "test"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("owner", ""));
             }
         }
 
@@ -111,16 +111,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepoCollaboratorsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.Add(null, "test","user1"));
-                Assert.Throws<ArgumentException>(() => client.Add("", "test", "user1"));
-                Assert.Throws<ArgumentNullException>(() => client.Add("owner", null, "user1"));
-                Assert.Throws<ArgumentException>(() => client.Add("owner", "", "user1"));
-                Assert.Throws<ArgumentException>(() => client.Add("owner", "test", ""));
-                Assert.Throws<ArgumentNullException>(() => client.Add("owner", "test", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Add(null, "test","user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Add("", "test", "user1"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Add("owner", null, "user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Add("owner", "", "user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Add("owner", "test", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Add("owner", "test", null));
             }
         }
 
@@ -137,16 +137,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepoCollaboratorsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.Delete(null, "test", "user1"));
-                Assert.Throws<ArgumentException>(() => client.Delete("", "test", "user1"));
-                Assert.Throws<ArgumentNullException>(() => client.Delete("owner", null, "user1"));
-                Assert.Throws<ArgumentException>(() => client.Delete("owner", "", "user1"));
-                Assert.Throws<ArgumentException>(() => client.Delete("owner", "test", ""));
-                Assert.Throws<ArgumentNullException>(() => client.Delete("owner", "test", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete(null, "test", "user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("", "test", "user1"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete("owner", null, "user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("owner", "", "user1"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("owner", "test", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete("owner", "test", null));
             }
         }
     }
diff --git a/Octokit.Tests/Clients/RepositoriesClientTests.cs b/Octokit.Tests/Clients/RepositoriesClientTests.cs
index 0f1329de..806f3e74 100644
--- a/Octokit.Tests/Clients/RepositoriesClientTests.cs
+++ b/Octokit.Tests/Clients/RepositoriesClientTests.cs
@@ -292,11 +292,11 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var reposEndpoint = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => reposEndpoint.GetAllForUser(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => reposEndpoint.GetAllForUser(null));
             }
         }
 
@@ -315,11 +315,11 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var reposEndpoint = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => reposEndpoint.GetAllForOrg(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => reposEndpoint.GetAllForOrg(null));
             }
         }
 
@@ -386,14 +386,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArguments()
+            public async Task EnsuresArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAllBranches(null, "repo"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAllBranches("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAllBranches("", "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAllBranches("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllBranches(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllBranches("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllBranches("", "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllBranches("owner", ""));
             }
         }
 
@@ -412,14 +412,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresArguments()
+            public async Task EnsuresArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAllContributors(null, "repo"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAllContributors("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAllContributors("", "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAllContributors("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllContributors(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllContributors("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllContributors("", "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllContributors("owner", ""));
             }
         }
 
@@ -438,14 +438,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAllLanguages(null, "repo"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAllLanguages("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAllLanguages("", "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAllLanguages("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllLanguages(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllLanguages("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllLanguages("", "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllLanguages("owner", ""));
             }
         }
 
@@ -464,14 +464,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAllTeams(null, "repo"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAllTeams("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAllTeams("", "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAllTeams("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllTeams(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllTeams("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllTeams("", "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllTeams("owner", ""));
             }
         }
 
@@ -490,14 +490,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAllTags(null, "repo"));
-                Assert.Throws<ArgumentNullException>(() => client.GetAllTags("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAllTags("", "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAllTags("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllTags(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllTags("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllTags("", "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllTags("owner", ""));
             }
         }
 
@@ -516,16 +516,16 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetBranch(null, "repo", "branch"));
-                Assert.Throws<ArgumentNullException>(() => client.GetBranch("owner", null, "branch"));
-                Assert.Throws<ArgumentNullException>(() => client.GetBranch("owner", "repo", null));
-                Assert.Throws<ArgumentException>(() => client.GetBranch("", "repo", "branch"));
-                Assert.Throws<ArgumentException>(() => client.GetBranch("owner", "", "branch"));
-                Assert.Throws<ArgumentException>(() => client.GetBranch("owner", "repo", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetBranch(null, "repo", "branch"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetBranch("owner", null, "branch"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetBranch("owner", "repo", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetBranch("", "repo", "branch"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetBranch("owner", "", "branch"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetBranch("owner", "repo", ""));
             }
         }
 
@@ -545,37 +545,37 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new RepositoriesClient(Substitute.For<IApiConnection>());
                 var update = new RepositoryUpdate();
 
-                Assert.Throws<ArgumentNullException>(() => client.Edit(null, "repo", update));
-                Assert.Throws<ArgumentNullException>(() => client.Edit("owner", null, update));
-                Assert.Throws<ArgumentNullException>(() => client.Edit("owner", "repo", null));
-                Assert.Throws<ArgumentException>(() => client.Edit("", "repo", update));
-                Assert.Throws<ArgumentException>(() => client.Edit("owner", "", update));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Edit(null, "repo", update));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Edit("owner", null, update));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Edit("owner", "repo", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Edit("", "repo", update));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Edit("owner", "", update));
             }
         }
 
         public class TheCompareMethod
         {
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var client = new RepositoryCommitsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.Compare(null, "repo", "base", "head"));
-                Assert.Throws<ArgumentException>(() => client.Compare("", "repo", "base", "head"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Compare(null, "repo", "base", "head"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Compare("", "repo", "base", "head"));
 
-                Assert.Throws<ArgumentNullException>(() => client.Compare("owner", null, "base", "head"));
-                Assert.Throws<ArgumentException>(() => client.Compare("owner", "", "base", "head"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Compare("owner", null, "base", "head"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Compare("owner", "", "base", "head"));
 
-                Assert.Throws<ArgumentNullException>(() => client.Compare("owner", "repo", null, "head"));
-                Assert.Throws<ArgumentException>(() => client.Compare("owner", "repo", "", "head"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Compare("owner", "repo", null, "head"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Compare("owner", "repo", "", "head"));
 
-                Assert.Throws<ArgumentNullException>(() => client.Compare("owner", "repo", "base", null));
-                Assert.Throws<ArgumentException>(() => client.Compare("owner", "repo", "base", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Compare("owner", "repo", "base", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Compare("owner", "repo", "base", ""));
             }
 
             [Fact]
@@ -608,18 +608,18 @@ namespace Octokit.Tests.Clients
         public class TheGetCommitMethod
         {
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var client = new RepositoryCommitsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.Get(null, "repo", "reference"));
-                Assert.Throws<ArgumentException>(() => client.Get("", "repo", "reference"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "repo", "reference"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", "repo", "reference"));
 
-                Assert.Throws<ArgumentNullException>(() => client.Get("owner", null, "reference"));
-                Assert.Throws<ArgumentException>(() => client.Get("owner", "", "reference"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, "reference"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Get("owner", "", "reference"));
 
-                Assert.Throws<ArgumentNullException>(() => client.Get("owner", "repo", null));
-                Assert.Throws<ArgumentException>(() => client.Get("owner", "repo", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", "repo", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Get("owner", "repo", ""));
             }
 
             [Fact]
@@ -638,17 +638,17 @@ namespace Octokit.Tests.Clients
         public class TheGetAllCommitsMethod
         {
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var client = new RepositoryCommitsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAll(null, "repo"));
-                Assert.Throws<ArgumentException>(() => client.GetAll("", "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("", "repo"));
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAll("owner", null));
-                Assert.Throws<ArgumentException>(() => client.GetAll("owner", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll("owner", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAll("owner", ""));
 
-                Assert.Throws<ArgumentNullException>(() => client.GetAll("owner", "repo", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAll("owner", "repo", null));
             }
 
             [Fact]
diff --git a/Octokit.Tests/Clients/RepositoryDeployKeysClientTests.cs b/Octokit.Tests/Clients/RepositoryDeployKeysClientTests.cs
index ab86ac63..5e7eb1e5 100644
--- a/Octokit.Tests/Clients/RepositoryDeployKeysClientTests.cs
+++ b/Octokit.Tests/Clients/RepositoryDeployKeysClientTests.cs
@@ -1,5 +1,6 @@
 using NSubstitute;
 using System;
+using System.Threading.Tasks;
 using Xunit;
 
 namespace Octokit.Tests.Clients
@@ -34,14 +35,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsureNonNullArguments()
+            public async Task EnsureNonNullArguments()
             {
                 var deployKeysClient = new RepositoryDeployKeysClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Get(null, "repo", 1));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Get("", "repo", 1));
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Get("user", null, 1));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Get("user", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Get(null, "repo", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Get("", "repo", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Get("user", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Get("user", "", 1));
             }
         }
 
@@ -59,14 +60,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var deployKeysClient = new RepositoryDeployKeysClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.GetAll(null, "repo"));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.GetAll("", "repo"));
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.GetAll("user", null));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.GetAll("user", ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.GetAll(null, "repo"));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.GetAll("", "repo"));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.GetAll("user", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.GetAll("user", ""));
             }
         }
 
@@ -85,18 +86,18 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var deployKeysClient = new RepositoryDeployKeysClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Create(null, "repo", new NewDeployKey()));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Create("", "repo", new NewDeployKey()));
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Create("user", null, new NewDeployKey()));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Create("user", "", new NewDeployKey()));
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Create("user", "repo", null));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey()));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey { Key = "ABC123" }));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey { Title = "user@repo" }));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Create(null, "repo", new NewDeployKey()));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Create("", "repo", new NewDeployKey()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Create("user", null, new NewDeployKey()));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Create("user", "", new NewDeployKey()));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Create("user", "repo", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey()));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey { Key = "ABC123" }));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Create("user", "repo", new NewDeployKey { Title = "user@repo" }));
             }
         }
 
@@ -114,14 +115,14 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var deployKeysClient = new RepositoryDeployKeysClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Delete(null, "repo", 1));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Delete("", "repo", 1));
-                Assert.Throws<ArgumentNullException>(() => deployKeysClient.Delete("user", null, 1));
-                Assert.Throws<ArgumentException>(() => deployKeysClient.Delete("user", "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Delete(null, "repo", 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Delete("", "repo", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => deployKeysClient.Delete("user", null, 1));
+                await Assert.ThrowsAsync<ArgumentException>(() => deployKeysClient.Delete("user", "", 1));
             }
         }
     }
diff --git a/Octokit.Tests/Clients/SearchClientTests.cs b/Octokit.Tests/Clients/SearchClientTests.cs
index 9f0ce20d..27f95d6f 100644
--- a/Octokit.Tests/Clients/SearchClientTests.cs
+++ b/Octokit.Tests/Clients/SearchClientTests.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using NSubstitute;
 using Xunit;
+using System.Threading.Tasks;
 
 namespace Octokit.Tests.Clients
 {
@@ -32,10 +33,10 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new SearchClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.SearchUsers(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.SearchUsers(null));
             }
 
             [Fact]
@@ -339,10 +340,10 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new SearchClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.SearchRepo(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.SearchRepo(null));
             }
 
             [Fact]
@@ -640,10 +641,10 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new SearchClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.SearchIssues(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.SearchIssues(null));
             }
 
             [Fact]
@@ -1177,10 +1178,10 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var client = new SearchClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.SearchCode(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.SearchCode(null));
             }
 
             [Fact]
diff --git a/Octokit.Tests/Clients/TeamsClientTests.cs b/Octokit.Tests/Clients/TeamsClientTests.cs
index ad022bdd..dfc65b51 100644
--- a/Octokit.Tests/Clients/TeamsClientTests.cs
+++ b/Octokit.Tests/Clients/TeamsClientTests.cs
@@ -35,11 +35,11 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var teams = new TeamsClient(Substitute.For<IApiConnection>());
 
-                Assert.Throws<ArgumentNullException>(() => teams.GetAll(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => teams.GetAll(null));
             }
         }
 
@@ -72,15 +72,15 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new TeamsClient(connection);
                 var team = new NewTeam("superstars");
 
-                Assert.Throws<ArgumentNullException>(() => client.Create(null, team));
-                Assert.Throws<ArgumentException>(() => client.Create("", team));
-                Assert.Throws<ArgumentNullException>(() => client.Create("name", null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, team));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", team));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("name", null));
             }
         }
 
@@ -99,12 +99,12 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArguments()
+            public async Task EnsuresNonNullArguments()
             {
                 var connection = Substitute.For<IApiConnection>();
                 var client = new TeamsClient(connection);
 
-                Assert.Throws<ArgumentNullException>(() => client.Update(1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Update(1, null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/UserEmailsClientTests.cs b/Octokit.Tests/Clients/UserEmailsClientTests.cs
index 7c095212..b3564796 100644
--- a/Octokit.Tests/Clients/UserEmailsClientTests.cs
+++ b/Octokit.Tests/Clients/UserEmailsClientTests.cs
@@ -1,6 +1,7 @@
 using NSubstitute;
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 using Xunit;
 
 namespace Octokit.Tests.Clients
@@ -37,17 +38,17 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArgument()
+            public async Task EnsuresNonNullArgument()
             {
                 var client = new UserEmailsClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.Add(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Add(null));
             }
 
             [Fact]
-            public void EnsuresNoNullEmails()
+            public async Task EnsuresNoNullEmails()
             {
                 var client = new UserEmailsClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentException>(() => client.Add("octokit@github.com", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Add("octokit@github.com", null));
             }
         }
 
@@ -66,17 +67,17 @@ namespace Octokit.Tests.Clients
             }
 
             [Fact]
-            public void EnsuresNonNullArgument()
+            public async Task EnsuresNonNullArgument()
             {
                 var client = new UserEmailsClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentNullException>(() => client.Delete(null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Delete(null));
             }
 
             [Fact]
-            public void EnsuresNoNullEmails()
+            public async Task EnsuresNoNullEmails()
             {
                 var client = new UserEmailsClient(Substitute.For<IApiConnection>());
-                Assert.Throws<ArgumentException>(() => client.Delete("octokit@github.com", null));
+                await Assert.ThrowsAsync<ArgumentException>(() => client.Delete("octokit@github.com", null));
             }
         }
 
diff --git a/Octokit.Tests/Helpers/AssertEx.cs b/Octokit.Tests/Helpers/AssertEx.cs
index ed388d23..6d5abe64 100644
--- a/Octokit.Tests/Helpers/AssertEx.cs
+++ b/Octokit.Tests/Helpers/AssertEx.cs
@@ -10,24 +10,6 @@ namespace Octokit.Tests.Helpers
 {
     public static class AssertEx
     {
-        public static void Empty<T>(IEnumerable<T> actual, string message)
-        {
-            var empty = Enumerable.Empty<T>();
-            WithMessage(() => Assert.Equal(empty, actual.ToArray()), message);
-        }
-
-        public static void WithMessage(Action assert, string message)
-        {
-            try
-            {
-                assert();
-            }
-            catch(AssertException ex)
-            {
-                throw new Exception(message, ex);
-            }
-        }
-
         public static void HasAttribute<TAttribute>(MemberInfo memberInfo, bool inherit = false) where TAttribute : Attribute
         {
             Assert.True(memberInfo.IsDefined(typeof(TAttribute), inherit), memberInfo.ToString() + Environment.NewLine);
diff --git a/Octokit.Tests/Models/PunchCardTests.cs b/Octokit.Tests/Models/PunchCardTests.cs
index 2e6493ba..3763d18e 100644
--- a/Octokit.Tests/Models/PunchCardTests.cs
+++ b/Octokit.Tests/Models/PunchCardTests.cs
@@ -27,7 +27,7 @@ public class PunchCardTests
         {
             IList<int> point1 = new[] { 1, 2, 3 };
             IEnumerable<IList<int>> points = new List<IList<int>> { point1 };
-            Assert.DoesNotThrow(() => new PunchCard(points));
+            var punchcard = new PunchCard(points);
         }
 
         [Fact]