public void testBooksGetAuthorByBookId() { //Arrange var BookRepoMockClass = new Mock <IBookRepo>(); string expected = "Huma"; BookRepoMockClass.Setup(x => x.GetAuthorByBookId(2)).Returns(expected); var booksController = new BooksController(BookRepoMockClass.Object); //Act IHttpActionResult result = booksController.GetAuthorByBookId(2); var resultBook = result as OkNegotiatedContentResult <string>; //Assert Assert.AreEqual(resultBook.Content, expected); }