public async Task EnsuresNonNullArguments()
            {
                var client = new ObservableOrganizationMembersClient(Substitute.For<IGitHubClient>());

                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Conceal(null, "username").ToTask());
                await Assert.ThrowsAsync<ArgumentException>(() => client.Conceal("", "username").ToTask());
                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Conceal("org", null).ToTask());
                await Assert.ThrowsAsync<ArgumentException>(() => client.Conceal("org", "").ToTask());
            }
            public void ConcealFromClientOrganizationMember()
            {
                var gitHubClient = Substitute.For<IGitHubClient>();
                var client = new ObservableOrganizationMembersClient(gitHubClient);

                client.Conceal("org", "user");

                gitHubClient.Organization.Member.Received().Conceal("org", "user");
            }