A simple kotlin class with mockito test caused Mis

问题:

I start to learn Kotlin and Mockito, so I code a simple module to test it.

AccountData_K.kt:

open class AccountData_K {
var isLogin: Boolean = false
var userName: String? = null

    fun changeLogin() : Boolean {
        return !isLogin
    }
}

AccountDataMockTest_K.kt:

class AccountDataMockTest_K {
    @Mock
    val accountData = AccountData_K()

    @Before
    fun setupAccountData() {
        MockitoAnnotations.initMocks(this)
    }

    @Test
    fun testNotNull() {
        assertNotNull(accountData)
    }

    @Test
    fun testIsLogin() {
        val result = accountData.changeLogin()
        assertEquals(result, true)
    }

    @Test
    fun testChangeLogin() {        
        `when`(accountData.changeLogin()).thenReturn(false)
        val result = accountData.changeLogin()
        assertEquals(result, false)
    }
}

And when I run the test, it reports an exception about the testChangeLogin() method:

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
2. inside when() you don't call method on mock but on some other object.
3. the parent of the mocked class is not public.
   It is a limitation of the mock engine.

at com.seal.materialdesignwithkotlin.AccountDataMockTest_K.testChangeLogin(AccountDataMockTest_K.kt:57)
...

I doubt why the method is not a method call on a mock...

So please help me, thanks.

回答1:

By default Kotlin's classes and members are final. Mockito is not able to mock final classes nor methods. To use Mockito you need to open the method you wish to mock:

open fun changeLogin() : Boolean {
    return !isLogin
}

Further reading

• Is it possible to use Mockito in Kotlin?
• Is it possible to use Mockito with Kotlin without open the class?

PS. In my humble opinion, as long as you keep you interfaces small through i.e ISP, a test code that uses Mockito or other mocking framework is rarely more readable and easy to understand than hand written fakes/stubs.

回答2:

As @miensol mentions, your problem occurs because the classes are final by default in Kotlin. The error message isn't very clear although this part mentions final as one of the possible causes:

1. you stub either of: final/private/equals()/hashCode() methods.

There is a project specifically to help deal with Kotlin "final by default" in unit testing with Mockito. For JUNIT, you can use the kotlin-testrunner which is an easy way to make any Kotlin test automatically open up classes for testing as they are loaded by the classloader. Usage is simple, just add one annotation of @RunWith(KotlinTestRunner::class), for example:

@RunWith(KotlinTestRunner::class)
class MyKotlinTestclass {
   @Test 
   fun test() {
   ...
   }
}

This is thoroughly covered in the article Never say final: mocking Kotlin classes in unit tests

This covers your use case in an automatic way by allowing all classes to be mocked that otherwise would not be allowed.