public async Task BeerExists_GivenAnNonExistingBeerId_ShouldReturnFalse() { //Arrange var guid = Guid.NewGuid(); var mockedBrandQuery = new Mock <IBrandQuery>(); mockedBrandQuery.Setup(query => query.GetBeer(It.IsAny <Guid>())) .ReturnsAsync((Beer)null); var brandValidation = new BrandValidation(mockedBrandQuery.Object); //Act var result = await brandValidation.BeerExists(guid); //Assert Assert.False(result); }