private void ExtractMmsiFromHtml_OnReceivedNullCollection_returnsZeroValue() { _creatorMock.Setup(mock => mock.CreateNodeCollection(It.IsAny <string>(), It.IsAny <string>())).Returns((HtmlNodeCollection)null); int result = _service.ExtractMmsiFromHtml("some_html"); Assert.Equal(0, result); _creatorMock.Verify(mock => mock.CreateNodeCollection(It.IsAny <string>(), It.IsAny <string>()), Times.Once); }