Fixing some unit tests that were not doing

any assertions.
Adding Received() where it was missing.
The majority of these instances were unawaited AssertEx.Throws
They are now all either awaited or replaced with Assert.Throw
Assert.Throw was used when possible and when not an option
AssertEx.Throw was awaited.

Octokit.Tests/Reactive/ObservableIssueCommentsClientTests.cs

@@ -47,7 +47,7 @@ namespace Octokit.Tests.Reactive
 
                 client.GetForRepository("fake", "repo");
 
-                gitHubClient.Connection.GetAsync<IReadOnlyList<GitHubClient>>(
+                gitHubClient.Connection.Received(1).GetAsync<List<IssueComment>>(
                     new Uri("repos/fake/repo/issues/comments", UriKind.Relative), null, null);
                 }
 
@@ -74,7 +74,7 @@ namespace Octokit.Tests.Reactive
 
                 client.GetForIssue("fake", "repo", 3);
 
-                gitHubClient.Connection.GetAsync<IReadOnlyList<GitHubClient>>(
+                gitHubClient.Connection.Received(1).GetAsync<List<IssueComment>>(
                     new Uri("repos/fake/repo/issues/3/comments", UriKind.Relative), null, null);
             }