Support mocking non-accessible parent methods

- Add support for mocking non-accessible parent methods using Mockk
- The class being mocked is always searched first for the specified
  method, then all superclasses are checked in no specific order. If
  multiple superclasses have matching signatures for the method then
  there is no guarantee which will be mocked first.
- Fixes mockk#425

dsl/jvm/src/main/kotlin/io/mockk/InternalPlatformDsl.kt

@@ -7,10 +7,12 @@ import java.lang.reflect.Method
 import java.util.concurrent.atomic.AtomicLong
 import kotlin.coroutines.Continuation
 import kotlin.reflect.KClass
+import kotlin.reflect.KFunction
 import kotlin.reflect.KMutableProperty1
 import kotlin.reflect.KProperty1
 import kotlin.reflect.KType
 import kotlin.reflect.KTypeParameter
+import kotlin.reflect.full.allSuperclasses
 import kotlin.reflect.full.functions
 import kotlin.reflect.full.memberProperties
 import kotlin.reflect.jvm.isAccessible
@@ -100,7 +102,7 @@ actual object InternalPlatformDsl {
         anyContinuationGen: () -> Continuation<*>
     ): Any? {
         val params = arrayOf(self, *args)
-        val func = self::class.functions.firstOrNull {
+        val func = self::class.allAncestorFunctions().firstOrNull {
             if (it.name != methodName) {
                 return@firstOrNull false
             }
@@ -134,6 +136,11 @@ actual object InternalPlatformDsl {
         }
     }
 
+    private fun KClass<*>.allAncestorFunctions(): Sequence<KFunction<*>> {
+        return (sequenceOf(this) + this.allSuperclasses.asSequence())
+            .flatMap { it.functions }
+    }
+
     private fun List<KType>.anyIsInstance(value: Any?): Boolean {
         return any { bound ->
             val classifier = bound.classifier

mockk/jvm/src/test/kotlin/io/mockk/it/PrivateParentMethodTest.kt

@@ -0,0 +1,66 @@
+package io.mockk.it
+
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.spyk
+import io.mockk.verify
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Test mocking non-visible parent methods through dynamic calls. Issue #425
+ */
+class PrivateParentMethodTest {
+    open class Parent {
+        open fun call(): String = callPrivate()
+        private fun callPrivate() = "Real"
+    }
+
+    open class Child: Parent()
+
+    class ChildWithShadowedMethod: Parent() {
+        override fun call(): String = callPrivate()
+        fun callPrivate() = "Shadowed"
+    }
+
+    class GrandChild: Child()
+
+    @Test
+    fun testChildAlwaysMockedFirst() {
+        val mock = mockk<ChildWithShadowedMethod> {
+            every { call() } answers { callOriginal() }
+            every { this@mockk["callPrivate"]() } returns "Mock"
+        }
+
+        assertEquals(mock.call(), "Mock")
+    }
+
+    @Test
+    fun testPrivateCallMock() {
+        val mock = mockk<Child> {
+            every { call() } answers { callOriginal() }
+            every { this@mockk["callPrivate"]() } returns "Mock"
+        }
+
+        assertEquals(mock.call(), "Mock")
+    }
+
+    @Test
+    fun testPrivateCallMockForGrandChild() {
+        val mock = mockk<GrandChild> {
+            every { call() } answers { callOriginal() }
+            every { this@mockk["callPrivate"]() } returns "Mock"
+        }
+
+        assertEquals(mock.call(), "Mock")
+    }
+
+    @Test
+    fun testPrivateCallVerify() {
+        val mock = spyk(Child(), recordPrivateCalls = true)
+
+        mock.call()
+
+        verify { mock["callPrivate"]() }
+    }
+}