feat: update spyOnProperty method, fixes #… (#5753)

* feat: update spyOnProperty method, fixes #5746

* changelog update for spyOnProperty, #5753

CHANGELOG.md

@@ -16,6 +16,8 @@
   ([#5670](https://github.com/facebook/jest/pull/5670))
 * `[expect]` Add inverse matchers (`expect.not.arrayContaining`, etc.,
   [#5517](https://github.com/facebook/jest/pull/5517))
+* `[jest-mock]` Update `spyOnProperty` to support spying on the prototype chain
+  ([#5753](https://github.com/facebook/jest/pull/5753))
 * `[jest-mock]` Add tracking of return values in the `mock` property
   ([#5752](https://github.com/facebook/jest/pull/5752))
 * `[jest-mock]` Add tracking of thrown errors in the `mock` property

packages/jest-mock/src/__tests__/jest_mock.test.js

@@ -900,5 +900,112 @@ describe('moduleMocker', () => {
       expect(spy1.mock.calls.length).toBe(1);
       expect(spy2.mock.calls.length).toBe(1);
     });
+
+    it('should work with getters on the prototype chain', () => {
+      let isOriginalCalled = false;
+      let originalCallThis;
+      let originalCallArguments;
+      const prototype = {
+        get method() {
+          return function() {
+            isOriginalCalled = true;
+            originalCallThis = this;
+            originalCallArguments = arguments;
+          };
+        },
+      };
+      const obj = Object.create(prototype, {});
+
+      const spy = moduleMocker.spyOn(obj, 'method', 'get');
+
+      const thisArg = {this: true};
+      const firstArg = {first: true};
+      const secondArg = {second: true};
+      obj.method.call(thisArg, firstArg, secondArg);
+      expect(isOriginalCalled).toBe(true);
+      expect(originalCallThis).toBe(thisArg);
+      expect(originalCallArguments.length).toBe(2);
+      expect(originalCallArguments[0]).toBe(firstArg);
+      expect(originalCallArguments[1]).toBe(secondArg);
+      expect(spy).toHaveBeenCalled();
+
+      isOriginalCalled = false;
+      originalCallThis = null;
+      originalCallArguments = null;
+      spy.mockReset();
+      spy.mockRestore();
+      obj.method.call(thisArg, firstArg, secondArg);
+      expect(isOriginalCalled).toBe(true);
+      expect(originalCallThis).toBe(thisArg);
+      expect(originalCallArguments.length).toBe(2);
+      expect(originalCallArguments[0]).toBe(firstArg);
+      expect(originalCallArguments[1]).toBe(secondArg);
+      expect(spy).not.toHaveBeenCalled();
+    });
+
+    test('should work with setters on the prototype chain', () => {
+      const prototype = {
+        _property: false,
+        set property(value) {
+          this._property = value;
+        },
+        get property() {
+          return this._property;
+        },
+      };
+      const obj = Object.create(prototype, {});
+
+      const spy = moduleMocker.spyOn(obj, 'property', 'set');
+      obj.property = true;
+      expect(spy).toHaveBeenCalled();
+      expect(obj.property).toBe(true);
+      obj.property = false;
+      spy.mockReset();
+      spy.mockRestore();
+      obj.property = true;
+      expect(spy).not.toHaveBeenCalled();
+      expect(obj.property).toBe(true);
+    });
+
+    it('supports restoring all spies on the prototype chain', () => {
+      let methodOneCalls = 0;
+      let methodTwoCalls = 0;
+      const prototype = {
+        get methodOne() {
+          return function() {
+            methodOneCalls++;
+          };
+        },
+        get methodTwo() {
+          return function() {
+            methodTwoCalls++;
+          };
+        },
+      };
+      const obj = Object.create(prototype, {});
+
+      const spy1 = moduleMocker.spyOn(obj, 'methodOne', 'get');
+      const spy2 = moduleMocker.spyOn(obj, 'methodTwo', 'get');
+
+      // First, we call with the spies: both spies and both original functions
+      // should be called.
+      obj.methodOne();
+      obj.methodTwo();
+      expect(methodOneCalls).toBe(1);
+      expect(methodTwoCalls).toBe(1);
+      expect(spy1.mock.calls.length).toBe(1);
+      expect(spy2.mock.calls.length).toBe(1);
+
+      moduleMocker.restoreAllMocks();
+
+      // Then, after resetting all mocks, we call methods again. Only the real
+      // methods should bump their count, not the spies.
+      obj.methodOne();
+      obj.methodTwo();
+      expect(methodOneCalls).toBe(2);
+      expect(methodTwoCalls).toBe(2);
+      expect(spy1.mock.calls.length).toBe(1);
+      expect(spy2.mock.calls.length).toBe(1);
+    });
   });
 });

packages/jest-mock/src/index.js

@@ -757,7 +757,13 @@ class ModuleMockerClass {
       throw new Error('No property name supplied');
     }
 
-    const descriptor = Object.getOwnPropertyDescriptor(obj, propertyName);
+    let descriptor = Object.getOwnPropertyDescriptor(obj, propertyName);
+    let proto = Object.getPrototypeOf(obj);
+
+    while (!descriptor && proto !== null) {
+      descriptor = Object.getOwnPropertyDescriptor(proto, propertyName);
+      proto = Object.getPrototypeOf(proto);
+    }
 
     if (!descriptor) {
       throw new Error(propertyName + ' property does not exist');