public async Task EnsureNonNullArguments()
            {
                var client = new ObservableCommitsClient(Substitute.For<IGitHubClient>());
                var newCommit = new NewCommit("message", "tree", new[] { "parent1", "parent2" });

                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create(null, "name", newCommit).ToTask());
                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", null, newCommit).ToTask());
                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("owner", "name", null).ToTask());
                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", "name", newCommit).ToTask());
                await Assert.ThrowsAsync<ArgumentException>(() => client.Create("owner", "", newCommit).ToTask());
            }
            public async Task RequestsCorrectUrl()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableCommitsClient(gitHubClient);
                var newCommit = new NewCommit("message", "tree", new[] { "parent1", "parent2" });

                client.Create("owner", "name", newCommit);

                gitHubClient.Git.Commit.Received().Create("owner", "name", newCommit);
            }
            public async Task PostsToTheCorrectUrlWithRepositoryId()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableCommitsClient(gitHubClient);

                var newCommit = new NewCommit("message", "tree", new[] { "parent1", "parent2" });

                client.Create(1, newCommit);

                gitHubClient.Git.Commit.Received().Create(1, newCommit);
            }