public void RequestsTheCorrectUrlWithRepositoryId()
            {
                var github = Substitute.For <IGitHubClient>();
                var client = new ObservableRepositoryBranchesClient(github);

                client.Get(1, "branch");

                github.Repository.Branch.Received(1).Get(1, "branch");
            }
            public async Task EnsuresNonNullArguments()
            {
                var client = new ObservableRepositoryBranchesClient(Substitute.For <IGitHubClient>());

                Assert.Throws <ArgumentNullException>(() => client.Get(null, "repo", "branch"));
                Assert.Throws <ArgumentNullException>(() => client.Get("owner", null, "branch"));
                Assert.Throws <ArgumentNullException>(() => client.Get("owner", "repo", null));

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

                Assert.Throws <ArgumentException>(() => client.Get("", "repo", "branch"));
                Assert.Throws <ArgumentException>(() => client.Get("owner", "", "branch"));
                Assert.Throws <ArgumentException>(() => client.Get("owner", "repo", ""));

                Assert.Throws <ArgumentException>(() => client.Get(1, ""));
            }