Implement spies for get/set functions on accessor properties

spec/core/SpyRegistrySpec.js

@@ -77,6 +77,126 @@ describe("SpyRegistry", function() {
     });
   });
 
+  describe("#spyOnProperty", function() {
+    // IE 8 doesn't support `definePropery` on non-DOM nodes
+    if (jasmine.getEnv().ieVersion < 9) { return; }
+
+    it("checks for the existence of the object", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry();
+      expect(function() {
+        spyRegistry.spyOnProperty(void 0, 'pants');
+      }).toThrowError(/could not find an object/);
+    });
+
+    it("checks that a property name was passed", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {};
+
+        expect(function() {
+          spyRegistry.spyOnProperty(subject);
+        }).toThrowError(/No property name supplied/);
+    });
+
+    it("checks for the existence of the method", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {};
+
+      expect(function() {
+        spyRegistry.spyOnProperty(subject, 'pants');
+      }).toThrowError(/property does not exist/);
+    });
+
+    it("checks for the existence of access type", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {};
+
+      Object.defineProperty(subject, 'pants', {
+        get: function() { return 1; },
+        configurable: true
+      });
+
+      expect(function() {
+        spyRegistry.spyOnProperty(subject, 'pants', 'set');
+      }).toThrowError(/does not have access type/);
+    });
+
+    it("checks if it has already been spied upon", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {};
+
+      Object.defineProperty(subject, 'spiedProp', {
+        get: function() { return 1; },
+        configurable: true
+      });
+
+      spyRegistry.spyOnProperty(subject, 'spiedProp');
+
+      expect(function() {
+        spyRegistry.spyOnProperty(subject, 'spiedProp');
+      }).toThrowError(/has already been spied upon/);
+    });
+
+    it("checks if it can be spied upon", function() {
+      var subject = {};
+
+      Object.defineProperty(subject, 'myProp', {
+        get: function() {}
+      });
+
+      Object.defineProperty(subject, 'spiedProp', {
+        get: function() {},
+        configurable: true
+      });
+
+      var spyRegistry = new jasmineUnderTest.SpyRegistry();
+
+      expect(function() {
+        spyRegistry.spyOnProperty(subject, 'myProp');
+      }).toThrowError(/is not declared configurable/);
+
+      expect(function() {
+        spyRegistry.spyOnProperty(subject, 'spiedProp');
+      }).not.toThrowError(/is not declared configurable/);
+    });
+
+    it("overrides the property getter on the object and returns the spy", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {},
+        returnValue = 1;
+
+      Object.defineProperty(subject, 'spiedProperty', {
+        get: function() { return returnValue; },
+        configurable: true
+      });
+
+      expect(subject.spiedProperty).toEqual(returnValue);
+
+      var spy = spyRegistry.spyOnProperty(subject, 'spiedProperty');
+      var getter = Object.getOwnPropertyDescriptor(subject, 'spiedProperty').get;
+
+      expect(getter).toEqual(spy);
+      expect(subject.spiedProperty).toBeUndefined();
+    });
+
+    it("overrides the property setter on the object and returns the spy", function() {
+      var spyRegistry = new jasmineUnderTest.SpyRegistry(),
+        subject = {},
+        returnValue = 1;
+
+      Object.defineProperty(subject, 'spiedProperty', {
+        get: function() { return returnValue; },
+        set: function() {},
+        configurable: true
+      });
+
+      var spy = spyRegistry.spyOnProperty(subject, 'spiedProperty', 'set');
+      var setter = Object.getOwnPropertyDescriptor(subject, 'spiedProperty').set;
+
+      expect(subject.spiedProperty).toEqual(returnValue);
+      expect(setter).toEqual(spy);
+    });
+  });
+
   describe("#clearSpies", function() {
     it("restores the original functions on the spied-upon objects", function() {
       var spies = [],
@@ -152,4 +272,51 @@ describe("SpyRegistry", function() {
       expect(jasmineUnderTest.isSpy(subject.spiedFunc)).toBe(false);
     });
   });
+
+    describe('spying on properties', function() {
+      it("restores the original properties on the spied-upon objects", function() {
+        // IE 8 doesn't support `definePropery` on non-DOM nodes
+        if (jasmine.getEnv().ieVersion < 9) { return; }
+
+        var spies = [],
+          spyRegistry = new jasmineUnderTest.SpyRegistry({currentSpies: function() { return spies; }}),
+          originalReturn = 1,
+          subject = {};
+
+        Object.defineProperty(subject, 'spiedProp', {
+          get: function() { return originalReturn; },
+          configurable: true
+        });
+
+        spyRegistry.spyOnProperty(subject, 'spiedProp');
+        spyRegistry.clearSpies();
+
+        expect(subject.spiedProp).toBe(originalReturn);
+      });
+
+      it("does not add a property that the spied-upon object didn't originally have", function() {
+        // IE 8 doesn't support `Object.create`
+        if (jasmine.getEnv().ieVersion < 9) { return; }
+
+        var spies = [],
+          spyRegistry = new jasmineUnderTest.SpyRegistry({currentSpies: function() { return spies; }}),
+          originalReturn = 1,
+          subjectParent = {};
+
+        Object.defineProperty(subjectParent, 'spiedProp', {
+          get: function() { return originalReturn; },
+          configurable: true
+        });
+
+        var subject = Object.create(subjectParent);
+
+        expect(subject.hasOwnProperty('spiedProp')).toBe(false);
+
+        spyRegistry.spyOnProperty(subject, 'spiedProp');
+        spyRegistry.clearSpies();
+
+        expect(subject.hasOwnProperty('spiedProp')).toBe(false);
+        expect(subject.spiedProp).toBe(originalReturn);
+      });
+    });
 });

spec/core/UtilSpec.js

@@ -25,4 +25,23 @@ describe("jasmineUnderTest.util", function() {
       expect(jasmineUnderTest.util.isUndefined(undefined)).toBe(false);
     });
   });
+
+  describe("getPropertyDescriptor", function() {
+    it("get property descriptor from object", function() {
+      var obj = {prop: 1},
+        actual = jasmineUnderTest.util.getPropertyDescriptor(obj, 'prop'),
+        expected = Object.getOwnPropertyDescriptor(obj, 'prop');
+
+      expect(actual).toEqual(expected);
+    });
+
+    it("get property descriptor from object property", function() {
+      var proto = {prop: 1},
+        obj = Object.create(proto),
+        actual = jasmineUnderTest.util.getPropertyDescriptor(proto, 'prop'),
+        expected = Object.getOwnPropertyDescriptor(proto, 'prop');
+
+      expect(actual).toEqual(expected);
+    });
+  });
 });

src/core/SpyRegistry.js

@@ -68,6 +68,66 @@ getJasmineRequireObj().SpyRegistry = function(j$) {
       return spiedMethod;
     };
 
+    this.spyOnProperty = function (obj, propertyName, accessType) {
+      accessType = accessType || 'get';
+
+      if (j$.util.isUndefined(obj)) {
+        throw new Error('spyOn could not find an object to spy upon for ' + propertyName + '');
+      }
+
+      if (j$.util.isUndefined(propertyName)) {
+        throw new Error('No property name supplied');
+      }
+
+      var descriptor;
+      try {
+        descriptor = j$.util.getPropertyDescriptor(obj, propertyName);
+      } catch(e) {
+        // IE 8 doesn't support `definePropery` on non-DOM nodes
+      }
+
+      if (!descriptor) {
+        throw new Error(propertyName + ' property does not exist');
+      }
+
+      if (!descriptor.configurable) {
+        throw new Error(propertyName + ' is not declared configurable');
+      }
+
+      if(!descriptor[accessType]) {
+        throw new Error('Property ' + propertyName + ' does not have access type ' + accessType);
+      }
+
+      if (j$.isSpy(descriptor[accessType])) {
+        //TODO?: should this return the current spy? Downside: may cause user confusion about spy state
+        throw new Error(propertyName + ' has already been spied upon');
+      }
+
+      var originalDescriptor = j$.util.clone(descriptor),
+        spy = j$.createSpy(propertyName, descriptor[accessType]),
+        restoreStrategy;
+
+      if (Object.prototype.hasOwnProperty.call(obj, propertyName)) {
+        restoreStrategy = function() {
+          Object.defineProperty(obj, propertyName, originalDescriptor);
+        };
+      } else {
+        restoreStrategy = function() {
+          delete obj[propertyName];
+        };
+      }
+
+      currentSpies().push({
+        restoreObjectToOriginalState: restoreStrategy
+      });
+
+      descriptor[accessType] = spy;
+
+      Object.defineProperty(obj, propertyName, descriptor);
+
+      return spy;
+    };
+
     this.clearSpies = function() {
       var spies = currentSpies();
       for (var i = spies.length - 1; i >= 0; i--) {

src/core/util.js

@@ -55,5 +55,17 @@ getJasmineRequireObj().util = function() {
     return cloned;
   };
 
+  util.getPropertyDescriptor = function(obj, methodName) {
+    var descriptor,
+      proto = obj;
+
+    do {
+      descriptor = Object.getOwnPropertyDescriptor(proto, methodName);
+      proto = Object.getPrototypeOf(proto);
+    } while (!descriptor && proto);
+
+    return descriptor;
+  };
+
   return util;
 };