How to use Mockito.mockStatic for mocking static methods in kotlin android

Question

How to use Mockito.mockStatic for mocking static methods in kotlin android ?

This is my code:

    class MyUtilClassTest {
       @Test
       fun testIsEnabled() {
          Mockito.mockStatic(MyUtilClass::class.java, Mockito.CALLS_REAL_METHODS)
                .use { mocked ->
                    mocked.`when`<Boolean> { MyUtilClass.isEnabled() }.thenReturn(true)
                    assertTrue(MyUtilClass.isEnabled())
                }
       }
    }
    
    object MyUtilClass {
       fun isEnabled(): Boolean = false
    }

I am getting this exception:

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:

you stub either of: final/private/equals()/hashCode() methods. Those methods cannot be stubbed/verified. Mocking methods declared on non-public parent classes is not supported.

inside when() you don't call method on mock but on some other object.

If your objective is to mock Kotlin objects, there's already an answer for that: https://stackoverflow.com/questions/37977320/how-to-mock-a-kotlin-singleton-object — Muhammad Faiq, Mar 29 '21 at 10:35

score 6 · Answer 1 · answered Apr 21 '21 at 08:26

If you annotate your function isEnabled with @JvmStatic, you won't get any error. As @Neige pointed out, static functions in Kotlin are actually not static in bytecode by default. Therefore, we need to mark our function with @JvmStatic in order to generate additional static getter/setter methods.

object MyUtilClass {
   @JvmStatic
   fun isEnabled(): Boolean = false
}

Neige · Answer 2 · 2021-03-29T10:36:18.877

2

From the JVM point of view MyUtilClass.isEnabled() is not a static class/function. You can use Show Kotlin Bytecode to understand what is behind

public final class MyUtilClass {
   public static final MyUtilClass INSTANCE;

   public final boolean isEnabled() {
      return false;
   }

   private MyUtilClass() {
   }

   static {
      MyUtilClass var0 = new MyUtilClass();
      INSTANCE = var0;
   }
}

edited Mar 29 '21 at 10:36

answered Mar 29 '21 at 10:28

Neige

2,770
2
15
21

How to use Mockito.mockStatic for mocking static methods in kotlin android

2 Answers2