public void CosmosService_Should_Return_DocumentId() { //Arrange var mockedRepo = new Mock <IGenericRepository <DocumentVm> >(); var sut = new CosmosService(mockedRepo.Object); var docVm = new DocumentVm { DocumentId = 123 }; mockedRepo.Setup(x => x.GetDocumentId(It.IsAny <string>())).Returns(docVm); //Act var guid = "abc-123"; var result = sut.GetDocumentId(guid); //Assert Assert.Equal(123, result); }