test_runner: ensure that mock.method works with class inheritance

Author: ErickWendel

lib/internal/test_runner/mock.js

@@ -174,19 +174,27 @@ class MockTracker {
 
       return original;
     }
-    let descriptor = ObjectGetOwnPropertyDescriptor(object, methodName);
-    let original = getOriginalObject(descriptor);
 
-    // classes instances
-    if (typeof original !== 'function') {
-      descriptor = ObjectGetOwnPropertyDescriptor(
-        ObjectGetPrototypeOf(object),
-        methodName
-      );
+    function findMethodOnPrototypeChain(instance, method, isDescriptor = false) {
+      const original = isDescriptor ?
+        instance :
+        ObjectGetOwnPropertyDescriptor(instance, method);
+
+      if (original && !isDescriptor) {
+        return original;
+      }
 
-      original = getOriginalObject(descriptor);
+      const proto = ObjectGetPrototypeOf(instance);
+      const desc = ObjectGetOwnPropertyDescriptor(proto, method);
+      if (!desc && proto.name) {
+        return findMethodOnPrototypeChain(proto, method, true);
+      }
+      return desc;
     }
 
+    const descriptor = findMethodOnPrototypeChain(object, methodName);
+    const original = getOriginalObject(descriptor);
+
     if (typeof original !== 'function') {
       throw new ERR_INVALID_ARG_VALUE(
         'methodName', original, 'must be a method'

test/parallel/test-runner-mocking.js

@@ -318,6 +318,7 @@ test('spy functions can be bound', (t) => {
   assert.strictEqual(sum.mock.restore(), undefined);
   assert.strictEqual(sum.bind(0)(2, 11), 13);
 });
+
 test('mocks prototype methods on an instance', async (t) => {
   class Runner {
     async someTask(msg) {
@@ -345,6 +346,13 @@ test('mocks prototype methods on an instance', async (t) => {
   assert.strictEqual(call.target, undefined);
   assert.strictEqual(call.this, obj);
 
+  const obj2 = new Runner();
+  // Ensure that a brand new instance is not mocked
+  assert.strictEqual(
+    obj2.someTask.mock,
+    undefined
+  );
+
   assert.strictEqual(obj.someTask.mock.restore(), undefined);
   assert.strictEqual(await obj.method(msg), msg);
   assert.strictEqual(obj.someTask.mock, undefined);
@@ -381,6 +389,42 @@ test('spies on async static class methods', async (t) => {
   assert.strictEqual(Runner.someTask.mock, undefined);
 });
 
+test('given null to a mock.method it throws a invalid argument error', (t) => {
+  assert.throws(() => t.mock.method(null, {}), /ERR_INVALID_ARG_TYPE/);
+});
+
+test('spy functions can be used on classes inheritance', (t) => {
+  class A {
+    static someTask(msg) {
+      return msg;
+    }
+    static method(msg) {
+      return this.someTask(msg);
+    }
+  }
+  class B extends A {}
+  class C extends B {}
+
+  const msg = 'ok';
+  assert.strictEqual(C.method(msg), msg);
+
+  t.mock.method(C, C.someTask.name);
+  assert.strictEqual(C.someTask.mock.calls.length, 0);
+
+  assert.strictEqual(C.method(msg), msg);
+
+  const call = C.someTask.mock.calls[0];
+
+  assert.deepStrictEqual(call.arguments, [msg]);
+  assert.strictEqual(call.result, msg);
+  assert.strictEqual(call.target, undefined);
+  assert.strictEqual(call.this, C);
+
+  assert.strictEqual(C.someTask.mock.restore(), undefined);
+  assert.strictEqual(C.method(msg), msg);
+  assert.strictEqual(C.someTask.mock, undefined);
+});
+
 test('mocked functions report thrown errors', (t) => {
   const testError = new Error('test error');
   const fn = t.mock.fn(() => {