public async Task EnsuresArgumentsNotNull()
{
var gitHubClient = Substitute.For<IGitHubClient>();
var client = new ObservableEventsClient(gitHubClient);
await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllIssuesForRepository(null, "name").ToTask());
await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllIssuesForRepository("", "name").ToTask());
await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllIssuesForRepository("owner", null).ToTask());
await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllIssuesForRepository("owner", "").ToTask());
}