public void ShouldSaveTagsInDb() { var linkRepo = Substitute.For <ILinksRepo>(); var webRepo = Substitute.For <IWebRepo>(); LinkProcessingService linkProcessingService = new LinkProcessingService(linkRepo, webRepo); List <string> testUrls = new List <string> { "https://en.wikipedia.org/wiki/Trololo" }; linkRepo.Contains(testUrls[0]).Returns(false); var testLink = new Link() { Url = testUrls[0], IterationId = 0 }; linkProcessingService.SaveTagsIntoDb(testUrls); linkRepo.Received(1).Contains(testUrls[0]); }