public async Task EnsuresArgumentsNotNull()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableIssueCommentsClient(gitHubClient);

                await AssertEx.Throws<ArgumentNullException>(async () => await client.GetForRepository(null, "name"));
                await AssertEx.Throws<ArgumentException>(async () => await client.GetForRepository("", "name"));
                await AssertEx.Throws<ArgumentNullException>(async () => await client.GetForRepository("owner", null));
                await AssertEx.Throws<ArgumentException>(async () => await client.GetForRepository("owner", ""));
            }
            public void RequestsCorrectUrl()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableIssueCommentsClient(gitHubClient);

                client.GetForRepository("fake", "repo");

                gitHubClient.Connection.Received(1).Get<List<IssueComment>>(
                    new Uri("repos/fake/repo/issues/comments", UriKind.Relative), null, null);
                }