public void GetPosts_invalideScreenName_ThrowException() { Mock.Get(_utilsCategory) .Setup(x => x.ResolveScreenName(It.IsAny <string>())) .Returns(() => null); _api.Invoking(x => x.GetPosts("someInvalideScreenName", 1)) .Should().Throw <Exception>() .WithMessage("Invalid screen name (id)."); Mock.Get(_utilsCategory) .Setup(x => x.ResolveScreenName(It.IsAny <string>())) .Returns(() => new VkObject { Id = null }); _api.Invoking(x => x.GetPosts("someInvalideScreenName", 1)) .Should().Throw <Exception>() .WithMessage("Invalid screen name (id)."); }