Remove support for stubbing undefined props (#1557)

This was a longer discussion that can be found in the
issues #1508, #1552 and #1537 - and internally amongst the core team.

Support for stubbing props using get()/set() was added in #1237
and also worked for undefined properties.

This type of behavior (stubbing undefined props) has been
explicitly disabled for sandboxes, so in order for Sinon to
behave in a consistent way, we should do the same here.

This change will bring normal stubs back to how it has
used to be historically, and will make sandbox stubs
and normal sinon stubs behave the same.

It might break things for people relying on the behavior
that has been present since Sinon 2.0, but it should
make things more reliable going forward.

lib/sinon/stub.js

@@ -9,6 +9,7 @@ var getPropertyDescriptor = require("./util/core/get-property-descriptor");
 var wrapMethod = require("./util/core/wrap-method");
 var stubEntireObject = require("./stub-entire-object");
 var throwOnFalsyObject = require("./throw-on-falsy-object");
+var valueToString = require("./util/core/value-to-string");
 
 var slice = Array.prototype.slice;
 
@@ -19,6 +20,10 @@ function stub(object, property) {
 
     throwOnFalsyObject.apply(null, arguments);
 
+    if (object && typeof property !== "undefined" && !(property in object)) {
+        throw new TypeError("Cannot stub non-existent own property " + valueToString(property));
+    }
+
     var actualDescriptor = getPropertyDescriptor(object, property);
     var isStubbingEntireObject = typeof property === "undefined" && typeof object === "object";
     var isCreatingNewStub = !object && typeof property === "undefined";

test/stub-test.js

@@ -5,7 +5,6 @@ var createStub = require("../lib/sinon/stub");
 var createStubInstance = require("../lib/sinon/stub").createStubInstance;
 var createSpy = require("../lib/sinon/spy");
 var sinonMatch = require("../lib/sinon/match");
-var getPropertyDescriptor = require("../lib/sinon/util/core/get-property-descriptor");
 var deprecated = require("../lib/sinon/util/core/deprecated");
 var assert = referee.assert;
 var refute = referee.refute;
@@ -1164,6 +1163,16 @@ describe("stub", function () {
 
             stub.restore();
         });
+
+        it("throws if stubbing non-existent property", function () {
+            var myObj = {};
+
+            assert.exception(function () {
+                createStub(myObj, "ouch");
+            });
+
+            refute.defined(myObj.ouch);
+        });
     });
 
     describe("stubbed function", function () {
@@ -2579,16 +2588,6 @@ describe("stub", function () {
             assert.equals(myObj.prop, "bar");
         });
 
-        it("can set getters for non-existing properties", function () {
-            var myObj = {};
-
-            createStub(myObj, "prop").get(function getterFn() {
-                return "bar";
-            });
-
-            assert.equals(myObj.prop, "bar");
-        });
-
         it("can restore stubbed setters for functions", function () {
             var propFn = function propFn() {
                 return "bar";
@@ -2627,19 +2626,6 @@ describe("stub", function () {
             assert.equals(myObj.prop, "bar");
         });
 
-        it("can restore stubbed getters for previously undefined properties", function () {
-            var myObj = {};
-
-            var stub = createStub(myObj, "nonExisting");
-
-            stub.get(function getterFn() {
-                return "baz";
-            });
-
-            stub.restore();
-
-            assert.equals(getPropertyDescriptor(myObj, "nonExisting"), undefined);
-        });
     });
 
     describe(".set", function () {
@@ -2689,18 +2675,6 @@ describe("stub", function () {
             assert.equals(myObj.example, "bar");
         });
 
-        it("can set setters for non-existing properties", function () {
-            var myObj = {};
-
-            createStub(myObj, "prop").set(function setterFn() {
-                myObj.example = "bar";
-            });
-
-            myObj.prop = "foo";
-
-            assert.equals(myObj.example, "bar");
-        });
-
         it("can restore stubbed setters for functions", function () {
             var propFn = function propFn() {
                 return "bar";
@@ -2741,19 +2715,6 @@ describe("stub", function () {
             assert.equals(myObj.otherProp, "bar");
         });
 
-        it("can restore stubbed setters for previously undefined properties", function () {
-            var myObj = {};
-
-            var stub = createStub(myObj, "nonExisting");
-
-            stub.set(function setterFn() {
-                myObj.otherProp = "baz";
-            });
-
-            stub.restore();
-
-            assert.equals(getPropertyDescriptor(myObj, "nonExisting"), undefined);
-        });
     });
 
     describe(".value", function () {
@@ -2777,15 +2738,6 @@ describe("stub", function () {
             assert.equals(myObj.prop, "rawString");
         });
 
-        it("allows restoring previously undefined properties", function () {
-            var obj = {};
-            var stub = createStub(obj, "nonExisting").value(2);
-
-            stub.restore();
-
-            assert.equals(getPropertyDescriptor(obj, "nonExisting"), undefined);
-        });
-
         it("allows stubbing function static properties", function () {
             var myFunc = function () {};
             myFunc.prop = "rawString";