public void CallPostServiceAllWithoutDeletedOnceWithEmptyString_WhenCalledWithEmptyString() { // Arrange var postEnumerable = new List <Post>() { new Post() }.AsEnumerable <Post>(); var postsServiceMock = new Mock <IPostService>(); postsServiceMock.Setup(m => m.AllWithoutDeleted(string.Empty)) .Returns(postEnumerable); PostController postController = new PostController(postsServiceMock.Object); // Act postController.FilteredPosts(string.Empty); // Assert postsServiceMock.Verify(m => m.AllWithoutDeleted(string.Empty), Times.Once); }