`clearInlineMocks` not working with `MockitoJUnit.rule()`

Hi !

I recenlty updated to 2.25.0 to make use of clearInlineMocks but I end up with NotAMockException when I use it in combination with MockitoJUnit.rule().

Eg

class ExampleUnitTest {

    @get:Rule
    val mockitoRule: MockitoRule = MockitoJUnit.rule()

    @Mock
    lateinit var state: MainState

    @After
    fun clearMocks() {
        Mockito.framework().clearInlineMocks()
    }

    @Test
    fun randomTest() {
		state.something
		Mockito.verify(state).something
    }
}

ends up with

org.mockito.exceptions.misusing.NotAMockException: Argument passed to Mockito.mockingDetails() should be a mock, but is an instance of class com.melih.playground.ui.main.state.MainState!

	at org.mockito.internal.junit.JUnitRule$1.evaluate(JUnitRule.java:49)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

and tests fail.

If I use @RunWith(MockitoJUnitRunner::class) tests pass, but I still get same exception at end of run.

If I remove rule & use MockitoAnnotations.initMocks(this) everything works fine.

[ZacSweers]

Wow, currently experiencing this XKCD comic. Thank you @ttanxu, that resolved our issue.

Worth noting that RuleChain for ordering is discouraged in Junit 4.13+, so using Rule’s ordering works instead

// Use Mockito's new strict stubs listener, which fails early on mismatched types.
// This also handles validating mocks and closing them after the test to prevent leaks.
@Rule(order = 0)
@JvmField
val mockitoRule: MockitoRule = MockitoJUnit.rule().strictness(Strictness.STRICT_STUBS)

// This needs to run _after_ mockitoRule is done
// https://github.com/mockito/mockito/issues/1902#issuecomment-727093806
@Rule(order = 1)
@JvmField
internal val clearInlineMocksRule: TestRule = ClearInlineMocksRule()

[ttanxu]

I have a theory, but I didn’t verify that explicitly so I might be wrong. Just to put this theory here to guide folks to a possible solution.

JUnit runs @Before after each rule, and @After before each rule. In this particular case clearInlineMocks() removed internal handlers of all inline mocks, but MockitoJUnit rule still needs to use them which made this exception.

The solution is to wrap clearInlineMocks() in a TestRule as well, and use RuleChain to make sure the order of those 2 rules.

I’ll leave it to Mockito team to decide if it should offer more guidance around the use of clearInlineMocks(), or even encapsulate the use of it into MockitoJUnit rule.