public void Should_ReturnMailMessageThunderbirdParser_WhenUserAgentContainsThunderBird() { //arrange var userAgent = "\r\nUser-Agent: Mozilla/5.0 (Windows NT 6.1; rv:14.0) Gecko/20120713 Thunderbird/14.0\r\n"; var mailMessageParserFactory = new MailMessageParserFactory(); //act var result=mailMessageParserFactory.GetMailMessageParser(userAgent) as MailMessageParserThunderbird; //assert result.Should().NotBeNull(); }