public void PrescriptionExistsTest() { int UserId = 1; var fakeRepositoryMock = new Mock <IPrescriptionRepository>(); fakeRepositoryMock.Setup(x => x.PrescriptionExists(UserId)).Returns(true); var prescriptionService = new PrescriptionService(fakeRepositoryMock.Object); var isExist = prescriptionService.PrescriptionExists(UserId); Assert.True(isExist); }