Update() public method

Updates a specified Issue Comment.
http://developer.github.com/v3/issues/comments/#edit-a-comment
public Update ( long repositoryId, int id, string commentUpdate ) : IObservable
repositoryId long The Id of the repository
id int The comment id
commentUpdate string The modified comment
return IObservable
            public async Task EnsuresNonNullArguments()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableIssueCommentsClient(gitHubClient);

                Assert.Throws<ArgumentNullException>(() => client.Update(null, "name", 42, "title"));
                Assert.Throws<ArgumentNullException>(() => client.Update("owner", null, 42, "x"));
                Assert.Throws<ArgumentNullException>(() => client.Update("owner", "name", 42, null));

                Assert.Throws<ArgumentNullException>(() => client.Update(1, 42, null));

                Assert.Throws<ArgumentException>(() => client.Update("", "name", 42, "x"));
                Assert.Throws<ArgumentException>(() => client.Update("owner", "", 42, "x"));
            }
            public void PostsToCorrectUrlWithRepositoryId()
            {
                const string issueCommentUpdate = "Worthwhile update";
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableIssueCommentsClient(gitHubClient);

                client.Update(1, 42, issueCommentUpdate);

                gitHubClient.Issue.Comment.Received().Update(1, 42, issueCommentUpdate);
            }