在 kotlin 中模拟伴随对象函数

我正在使用PowerMock和RoboElectric，我想为一个类模拟一个配套的对象函数.当我这样做时，我得到一个错误:

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);

我基本上是这样的:

open class MockableClass private constructor(context: Context) {

    companion object {

        private val INSTANCE_LOCK = Any()
        private var sInstance: MockableClass? = null

        @JvmStatic
        fun getInstance(context: Context): MockableClass? {
            synchronized(INSTANCE_LOCK) {
                sInstance = (sInstance ?: MockableClass(context).let {
                    if (it.isValid) it
                    else null
                }
            }
            return sInstance
        }
    }

    init {
        // Do some initialization using context...
        // Set isValid to true/false depending on success
    }

    val isValid: Boolean
}

当我go 测试它时，我会假设它总是可以工作的，并且希望getInstance只返回MockableClass的模拟版本.

@RunWith(RobolectricTestRunner::class)
@Config(manifest = "src/main/AndroidManifest.xml",
        constants = BuildConfig::class,
        sdk = intArrayOf(23))
@PowerMockIgnore("org.mockito.*", "org.robolectric.*", "android.*")
@PrepareForTest(MockableClass::class)
class MyTest {

    private lateinit var context: Context

    @get:Rule
    val rule = PowerMockRule()

    @Before
    fun setUp() {
        context = RuntimeEnvironment.application as Context
    }

    @Test
    fun test() {
        val instance = mock(MockableClass::class.java)
        mockStatic(MockableClass::class.java)
        `when`(MockableClass.getInstance(Matchers.isA(Context::class.java)))
                .thenReturn(instance)
        assertEquals(instance,
                MockableClass.getInstance(RuntimeEnvironment.application as Context))
    }
}

I've also tried mocking MockableClass.Companion::class.java with no luck.

有人知道我需要做什么才能模拟这个getInstance功能吗？