Ensure user agent not empty string

Also added more ctor tests

Octokit.Tests/Http/ConnectionTests.cs

@@ -9,7 +9,6 @@ using NSubstitute;
 using Octokit.Http;
 using Octokit.Tests.Helpers;
 using Xunit;
-using Xunit.Extensions;
 
 namespace Octokit.Tests.Http
 {
@@ -18,25 +17,6 @@ namespace Octokit.Tests.Http
         const string ExampleUrl = "http://example.com";
         static readonly Uri ExampleUri = new Uri(ExampleUrl);
 
-        public class TheConstructor
-        {
-            [Fact]
-            public void EnsuresAbsoluteBaseAddress()
-            {
-                Assert.Throws<ArgumentException>(() => new Connection("Test Runner", new Uri("/foo", UriKind.Relative)));
-                Assert.Throws<ArgumentException>(() => new Connection("Test Runner", new Uri("/foo", UriKind.RelativeOrAbsolute)));
-            }
-
-            [Fact]
-            public void CreatesConnectionWithBaseAddress()
-            {
-                var connection = new Connection("Test Runner User Agent", new Uri("https://github.com/"));
-                
-                Assert.Equal(new Uri("https://github.com/"), connection.BaseAddress);
-                Assert.Equal("Test Runner User Agent", connection.UserAgent);
-            }
-        }
-
         public class TheGetAsyncMethod
         {
             [Fact]
@@ -271,5 +251,84 @@ namespace Octokit.Tests.Http
                         req.Endpoint == new Uri("/endpoint", UriKind.Relative)));
             }
         }
+
+        public class TheConstructor
+        {
+            [Fact]
+            public void EnsuresAbsoluteBaseAddress()
+            {
+                Assert.Throws<ArgumentException>(() => new Connection("Test Runner", new Uri("/foo", UriKind.Relative)));
+                Assert.Throws<ArgumentException>(() => new Connection("Test Runner", new Uri("/foo", UriKind.RelativeOrAbsolute)));
+            }
+
+            [Fact]
+            public void EnsuresNonNullArguments()
+            {
+                // 1 arg
+                Assert.Throws<ArgumentNullException>(() => new Connection(null));
+                Assert.Throws<ArgumentException>(() => new Connection(""));
+
+                
+                // 2 args
+                Assert.Throws<ArgumentNullException>(() => new Connection(null, new Uri("https://example.com"))); 
+                Assert.Throws<ArgumentException>(() => new Connection("", new Uri("https://example.com")));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo", (Uri)null));
+
+                // 3 args
+                Assert.Throws<ArgumentException>(() => new Connection("",
+                    new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>())); 
+                Assert.Throws<ArgumentNullException>(() => new Connection(null,
+                    new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>()));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    null,
+                    Substitute.For<ICredentialStore>()));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    new Uri("https://example.com"),
+                    null));
+
+                // 5 Args
+                Assert.Throws<ArgumentException>(() => new Connection(""
+                    , new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>(),
+                    Substitute.For<IHttpClient>(),
+                    Substitute.For<IJsonSerializer>())); 
+                Assert.Throws<ArgumentNullException>(() => new Connection(null
+                    , new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>(),
+                    Substitute.For<IHttpClient>(),
+                    Substitute.For<IJsonSerializer>())); 
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>(),
+                    Substitute.For<IHttpClient>(),
+                    null));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    new Uri("https://example.com"),
+                    Substitute.For<ICredentialStore>(),
+                    null,
+                    Substitute.For<IJsonSerializer>()));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    new Uri("https://example.com"),
+                    null,
+                    Substitute.For<IHttpClient>(),
+                    Substitute.For<IJsonSerializer>()));
+                Assert.Throws<ArgumentNullException>(() => new Connection("foo",
+                    null,
+                    Substitute.For<ICredentialStore>(),
+                    Substitute.For<IHttpClient>(),
+                    Substitute.For<IJsonSerializer>()));
+            }
+
+            [Fact]
+            public void CreatesConnectionWithBaseAddress()
+            {
+                var connection = new Connection("Test Runner User Agent", new Uri("https://github.com/"));
+
+                Assert.Equal(new Uri("https://github.com/"), connection.BaseAddress);
+                Assert.Equal("Test Runner User Agent", connection.UserAgent);
+            }
+        }
     }
 }

Octokit/Http/Connection.cs

@@ -44,7 +44,7 @@ namespace Octokit.Http
             IHttpClient httpClient,
             IJsonSerializer serializer)
         {
-            Ensure.ArgumentNotNull(userAgent, "userAgent");
+            Ensure.ArgumentNotNullOrEmptyString(userAgent, "userAgent");
             Ensure.ArgumentNotNull(baseAddress, "baseAddress");
             Ensure.ArgumentNotNull(credentialStore, "credentialStore");
             Ensure.ArgumentNotNull(httpClient, "httpClient");