public async Task ApplyThrowsArgumentNullExceptionWhenSourceSequenceIsNull() { IAsyncEnumerable <string> source = null; Exception exception = null; try { int length = 0; source.ShouldBeNull(); await source.ApplyAsync(s => length += s.Length); } catch (Exception e) { exception = e; } exception.ShouldNotBeNull(); exception.ShouldBeOfType <ArgumentNullException>(); }