test: fix mock.method to support class instances

It fixes a problem when trying to spy a method from a class instance or static functions on a class instance PR-URL: nodejs/node#45608 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com> (cherry picked from commit 929aada39d0f418193ca03cc360ced8c5b4ce553)
nodejs · MoLow · Feb 2, 2023 · Aug 2, 2022 · Aug 15, 2022 · Sep 4, 2022
commit 9fa496b0298a9ead260070bc548291f571840c70
diff --git a/lib/internal/per_context/primordials.js b/lib/internal/per_context/primordials.js
@@ -40,6 +40,7 @@ exports.ObjectDefineProperty = (obj, key, descr) => Object.defineProperty(obj, k
 exports.ObjectEntries = obj => Object.entries(obj)
 exports.ObjectFreeze = obj => Object.freeze(obj)
 exports.ObjectGetOwnPropertyDescriptor = (obj, key) => Object.getOwnPropertyDescriptor(obj, key)
+exports.ObjectGetPrototypeOf = obj => Object.getPrototypeOf(obj)
 exports.ObjectIsExtensible = obj => Object.isExtensible(obj)
 exports.ObjectPrototypeHasOwnProperty = (obj, property) => Object.prototype.hasOwnProperty.call(obj, property)
 exports.ObjectSeal = (obj) => Object.seal(obj)

diff --git a/lib/internal/test_runner/mock.js b/lib/internal/test_runner/mock.js
@@ -1,4 +1,4 @@
-// https://github.com/nodejs/node/blob/afed1afa55962211b6b56c2068d520b4d8a08888/lib/internal/test_runner/mock.js
+// https://github.com/nodejs/node/blob/929aada39d0f418193ca03cc360ced8c5b4ce553/lib/internal/test_runner/mock.js
 'use strict'
 const {
   ArrayPrototypePush,
@@ -7,6 +7,7 @@ const {
   FunctionPrototypeCall,
   ObjectDefineProperty,
   ObjectGetOwnPropertyDescriptor,
+  ObjectGetPrototypeOf,
   Proxy,
   ReflectApply,
   ReflectConstruct,
@@ -127,13 +128,15 @@ class MockTracker {
   }
 
   method (
-    object,
+    objectOrFunction,
     methodName,
     implementation = kDefaultFunction,
     options = kEmptyObject
   ) {
-    validateObject(object, 'object')
     validateStringOrSymbol(methodName, 'methodName')
+    if (typeof objectOrFunction !== 'function') {
+      validateObject(objectOrFunction, 'object')
+    }
 
     if (implementation !== null && typeof implementation === 'object') {
       options = implementation
@@ -158,8 +161,8 @@ class MockTracker {
         'options.setter', setter, "cannot be used with 'options.getter'"
       )
     }
+    const descriptor = findMethodOnPrototypeChain(objectOrFunction, methodName)
 
-    const descriptor = ObjectGetOwnPropertyDescriptor(object, methodName)
     let original
 
     if (getter) {
@@ -176,7 +179,7 @@ class MockTracker {
       )
     }
 
-    const restore = { descriptor, object, methodName }
+    const restore = { descriptor, object: objectOrFunction, methodName }
     const impl = implementation === kDefaultFunction
       ? original
       : implementation
@@ -199,7 +202,7 @@ class MockTracker {
       mockDescriptor.value = mock
     }
 
-    ObjectDefineProperty(object, methodName, mockDescriptor)
+    ObjectDefineProperty(objectOrFunction, methodName, mockDescriptor)
 
     return mock
   }
@@ -348,4 +351,21 @@ function validateTimes (value, name) {
   validateInteger(value, name, 1)
 }
 
+function findMethodOnPrototypeChain (instance, methodName) {
+  let host = instance
+  let descriptor
+
+  while (host !== null) {
+    descriptor = ObjectGetOwnPropertyDescriptor(host, methodName)
+
+    if (descriptor) {
+      break
+    }
+
+    host = ObjectGetPrototypeOf(host)
+  }
+
+  return descriptor
+}
+
 module.exports = { MockTracker }
diff --git a/test/parallel/test-runner-mocking.js b/test/parallel/test-runner-mocking.js
@@ -1,4 +1,4 @@
-// https://github.com/nodejs/node/blob/afed1afa55962211b6b56c2068d520b4d8a08888/test/parallel/test-runner-mocking.js
+// https://github.com/nodejs/node/blob/929aada39d0f418193ca03cc360ced8c5b4ce553/test/parallel/test-runner-mocking.js
 'use strict'
 const common = require('../common')
 const assert = require('node:assert')
@@ -320,6 +320,156 @@ test('spy functions can be bound', (t) => {
   assert.strictEqual(sum.bind(0)(2, 11), 13)
 })
 
+test('mocks prototype methods on an instance', async (t) => {
+  class Runner {
+    async someTask (msg) {
+      return Promise.resolve(msg)
+    }
+
+    async method (msg) {
+      await this.someTask(msg)
+      return msg
+    }
+  }
+  const msg = 'ok'
+  const obj = new Runner()
+  assert.strictEqual(await obj.method(msg), msg)
+
+  t.mock.method(obj, obj.someTask.name)
+  assert.strictEqual(obj.someTask.mock.calls.length, 0)
+
+  assert.strictEqual(await obj.method(msg), msg)
+
+  const call = obj.someTask.mock.calls[0]
+
+  assert.deepStrictEqual(call.arguments, [msg])
+  assert.strictEqual(await call.result, msg)
+  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)
+  assert.strictEqual(Runner.prototype.someTask.mock, undefined)
+})
+
+test('spies on async static class methods', async (t) => {
+  class Runner {
+    static async someTask (msg) {
+      return Promise.resolve(msg)
+    }
+
+    static async method (msg) {
+      await this.someTask(msg)
+      return msg
+    }
+  }
+  const msg = 'ok'
+  assert.strictEqual(await Runner.method(msg), msg)
+
+  t.mock.method(Runner, Runner.someTask.name)
+  assert.strictEqual(Runner.someTask.mock.calls.length, 0)
+
+  assert.strictEqual(await Runner.method(msg), msg)
+
+  const call = Runner.someTask.mock.calls[0]
+
+  assert.deepStrictEqual(call.arguments, [msg])
+  assert.strictEqual(await call.result, msg)
+  assert.strictEqual(call.target, undefined)
+  assert.strictEqual(call.this, Runner)
+
+  assert.strictEqual(Runner.someTask.mock.restore(), undefined)
+  assert.strictEqual(await Runner.method(msg), msg)
+  assert.strictEqual(Runner.someTask.mock, undefined)
+  assert.strictEqual(Runner.prototype.someTask, undefined)
+})
+
+test('given null to a mock.method it throws a invalid argument error', (t) => {
+  assert.throws(() => t.mock.method(null, {}), { code: 'ERR_INVALID_ARG_TYPE' })
+})
+
+test('it should throw given an inexistent property on a object instance', (t) => {
+  assert.throws(() => t.mock.method({ abc: 0 }, 'non-existent'), {
+    code: 'ERR_INVALID_ARG_VALUE'
+  })
+})
+
+test('spy functions can be used on classes inheritance', (t) => {
+  // Makes sure that having a null-prototype doesn't throw our system off
+  class A extends null {
+    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('spy functions don\'t affect the prototype chain', (t) => {
+  class A {
+    static someTask (msg) {
+      return msg
+    }
+  }
+  class B extends A {}
+  class C extends B {}
+
+  const msg = 'ok'
+
+  const ABeforeMockIsUnchanged = Object.getOwnPropertyDescriptor(A, A.someTask.name)
+  const BBeforeMockIsUnchanged = Object.getOwnPropertyDescriptor(B, B.someTask.name)
+  const CBeforeMockShouldNotHaveDesc = Object.getOwnPropertyDescriptor(C, C.someTask.name)
+
+  t.mock.method(C, C.someTask.name)
+  C.someTask(msg)
+  const BAfterMockIsUnchanged = Object.getOwnPropertyDescriptor(B, B.someTask.name)
+
+  const AAfterMockIsUnchanged = Object.getOwnPropertyDescriptor(A, A.someTask.name)
+  const CAfterMockHasDescriptor = Object.getOwnPropertyDescriptor(C, C.someTask.name)
+
+  assert.strictEqual(CBeforeMockShouldNotHaveDesc, undefined)
+  assert.ok(CAfterMockHasDescriptor)
+
+  assert.deepStrictEqual(ABeforeMockIsUnchanged, AAfterMockIsUnchanged)
+  assert.strictEqual(BBeforeMockIsUnchanged, BAfterMockIsUnchanged)
+  assert.strictEqual(BBeforeMockIsUnchanged, undefined)
+
+  assert.strictEqual(C.someTask.mock.restore(), undefined)
+  const CAfterRestoreKeepsDescriptor = Object.getOwnPropertyDescriptor(C, C.someTask.name)
+  assert.ok(CAfterRestoreKeepsDescriptor)
+})
+
 test('mocked functions report thrown errors', (t) => {
   const testError = new Error('test error')
   const fn = t.mock.fn(() => {