public void FindByLastName_ReturnsDoctors_WhenCalled([NotNull] IDoctor doctor) { // Arrange var repository = Substitute.For <IDoctorsRepository>(); repository.FindByLastName(Arg.Any <string>()).Returns(CreateList); InformationFinder sut = CreateSut(repository); // Act IEnumerable <IDoctorForResponse> actual = sut.FindByLastName("any name"); // Assert Assert.Equal(2, actual.Count()); }