Mocking static classes with Powermock2 and Kotlin : <p>in Android I've been using the version <strong>1.6.1</strong> of Powermock and all this implementation worked really good for statics.
It's not working now at all when I changed to <strong>2.0.0-beta.5</strong>. Indeed, it didn't even work upgrading from my previous <strong>1.6.1</strong> to <strong>1.7.1</strong>.</p>

<p>I have this implementation:</p>

<pre><code>// Power Mockito
testImplementation "org.powermock:powermock-api-mockito2:2.0.0-beta.5"
testImplementation "org.powermock:powermock-module-junit4-rule-agent:2.0.0-beta.5"
testImplementation "org.powermock:powermock-module-junit4:2.0.0-beta.5"
//testImplementation 'org.powermock:powermock-module-junit4-rule:2.0.0-beta.5'

// Mockito
testImplementation "org.mockito:mockito-core:2.11.0"
testImplementation "com.nhaarman:mockito-kotlin-kt1.1:1.5.0"
androidTestImplementation("com.nhaarman:mockito-kotlin-kt1.1:1.5.0", {
    exclude group: 'org.mockito', module: 'mockito-core'
})
androidTestImplementation 'org.mockito:mockito-android:2.11.0'
</code></pre>

<p>and I'm trying to mock a static the same way I was doing with <strong>1.6.1:</strong></p>

<pre><code>@RunWith(PowerMockRunner::class)
@PrepareForTest(SharedPreferencesHelper.Companion::class, ConfigUseCaseTests::class)
class ConfigUseCaseTests {

    lateinit var context: Context

    @Before
    fun setUp() {
        context = mock()
    }

    @Test
    fun getConfigs_fromJson() {
        PowerMockito.mockStatic(SharedPreferencesHelper.Companion::class.java)

        val instance = mock&lt;SharedPreferencesHelper.Companion&gt;()
        doReturn("foo")
                .whenever(instance)
                .loadString(isA(), anyString(), anyString(), anyString())
//        whenever(instance.loadString(isA(), anyString(), anyString(), anyString())).thenReturn("foo") // This shows the same error
        PowerMockito.whenNew(SharedPreferencesHelper.Companion::class.java)
                .withAnyArguments()
                .thenReturn(instance)

        val mockedFoo = instance.loadString(context, "", "", "") // This shows "foo"

        val mockedCompanion = SharedPreferencesHelper.loadString(context, "", "", "") // This is throwing NullPointerException

        Assert.assertEquals(mockedCompanion, "foo")
    }
}
</code></pre>

<p>My <strong>SharedPreferencesHelper</strong> looks like:</p>

<pre><code>class SharedPreferencesHelper {
    companion object {

        @Suppress("NON_FINAL_MEMBER_IN_OBJECT")
        open fun loadString(context: Context, fileName: String, key: String, defaultValue: String?): String? {
            val sharedPreferences = getWithFileName(context, fileName)
            return if (!sharedPreferences.contains(key)) {
                defaultValue
            } else {
                sharedPreferences.getString(key, defaultValue)
            }
        }
    }
}
</code></pre>

<p>I've tried to play with the <code>open</code> but it didn't work.</p>

<p><strong>Exception:</strong> (I don't understand it at all)</p>

<pre><code>java.lang.NullPointerException
    at my.package.ConfigUseCaseTests.getConfigs_fromJson(ConfigUseCaseTests.kt:45)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:326)
    at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:89)
    at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:97)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:310)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:131)
</code></pre>

<p>I can say, sometimes IT WORKS!! I'm adding the video because it looks amazing that it happens just sometimes:
<a href="https://youtu.be/YZObVLcERBo" rel="noreferrer">https://youtu.be/YZObVLcERBo</a> (watch at the middle and the end)</p>
