diff --git a/Octokit.Tests/Octokit.Tests.csproj b/Octokit.Tests/Octokit.Tests.csproj
index 5c6484c3..9f226d4e 100644
--- a/Octokit.Tests/Octokit.Tests.csproj
+++ b/Octokit.Tests/Octokit.Tests.csproj
@@ -212,6 +212,7 @@
     <Compile Include="Reactive\ObservableReleasesClientTests.cs" />
     <Compile Include="Reactive\ObservablePullRequestReviewCommentsClientTests.cs" />
     <Compile Include="Reactive\ObservableRepositoriesClientTests.cs" />
+    <Compile Include="Reactive\ObservableRepositoryCommitsClientTests.cs" />
     <Compile Include="Reactive\ObservableRepositoryDeployKeysClientTests.cs" />
     <Compile Include="Reactive\ObservableGistsTests.cs" />
     <Compile Include="Reactive\ObservableStarredClientTests.cs" />
diff --git a/Octokit.Tests/Reactive/ObservableRepositoryCommitsClientTests.cs b/Octokit.Tests/Reactive/ObservableRepositoryCommitsClientTests.cs
new file mode 100644
index 00000000..a99938b4
--- /dev/null
+++ b/Octokit.Tests/Reactive/ObservableRepositoryCommitsClientTests.cs
@@ -0,0 +1,50 @@
+using System;
+using System.Reactive.Threading.Tasks;
+using System.Threading.Tasks;
+using NSubstitute;
+using Octokit.Reactive;
+using Xunit;
+
+namespace Octokit.Tests.Reactive
+{
+    public class ObservableRepositoryCommitsClientTests
+    {
+        public class TheGetSha1Method
+        {
+            [Fact]
+            public void EnsuresNonNullArguments()
+            {
+                var client = new ObservableRepositoryCommitsClient(Substitute.For<IGitHubClient>());
+
+                Assert.ThrowsAsync<ArgumentException>(() => client.GetSha1("", "name", "reference").ToTask());
+                Assert.ThrowsAsync<ArgumentException>(() => client.GetSha1("owner", "", "reference").ToTask());
+                Assert.ThrowsAsync<ArgumentException>(() => client.GetSha1("owner", "name", "").ToTask());
+            }
+
+            [Fact]
+            public async Task EnsuresNonEmptyArguments()
+            {
+                var client = new ObservableRepositoryCommitsClient(Substitute.For<IGitHubClient>());
+
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetSha1(null, "name", "reference").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetSha1("owner", null, "reference").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetSha1("owner", "name", null).ToTask());
+            }
+
+            [Fact]
+            public void GetsCorrectUrl()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableRepositoryCommitsClient(gitHubClient);
+
+                client.GetSha1("owner", "name", "reference");
+
+                gitHubClient
+                    .Received()
+                    .Repository
+                    .Commit
+                    .GetSha1("owner", "name", "reference");
+            }
+        }
+    }
+}