class ClassToTest {
  private fun privateMethod(text: String): String {
    return "Hello $text"
  }
}

class TestClass {

   @Before
   fun setup() {
      MockitoAnnotations.openMocks(this)
   }

   @Test
   fun testSplitNumbers() {
      val clazz = spyk<ClassToTest>()

      val method = clazz.javaClass.getDeclaredMethod("privateMethod", String::class.java)
      method.isAccessible = true
      val result = method.invoke(clazz, "Test") as? String
      Assert.assertEquals("Hello Test", result)
   }
}