Remove undesirable methods before returning fake

lib/sinon/fake.js

@@ -6,44 +6,71 @@ function getError(value) {
     return value instanceof Error ? value : new Error(value);
 }
 
+function cleanProxy(f) {
+    var undesirableProperties = [
+        "instantiateFake",
+        "callArg",
+        "callArgOn",
+        "callArgOnWith",
+        "callArgWith",
+        "invokeCallback",
+        "throwArg",
+        "withArgs",
+        "yield",
+        "yieldOn",
+        "yieldTo",
+        "yieldToOn"
+    ];
+
+    undesirableProperties.forEach(function (key) {
+        delete f[key];
+    });
+
+    return f;
+}
+
+function wrapFunc(f) {
+    return cleanProxy(spy(f));
+}
+
 function fake(f) {
     if (typeof func !== "undefined" && typeof func !== "function") {
         throw new TypeError("Expected func argument to be a Function");
     }
 
-    return spy(f);
+    return wrapFunc(f);
 }
 
 fake.returns = function returns(value) {
     function f() {
         return value;
     }
 
-    return spy(f);
+    return wrapFunc(f);
 };
 
 fake.throws = function throws(value) {
     function f() {
         throw getError(value);
     }
 
-    return spy(f);
+    return wrapFunc(f);
 };
 
 fake.resolves = function resolves(value) {
     function f() {
         return Promise.resolve(value);
     }
 
-    return spy(f);
+    return wrapFunc(f);
 };
 
 fake.rejects = function rejects(value) {
     function f() {
         return Promise.reject(getError(value));
     }
 
-    return spy(f);
+    return wrapFunc(f);
 };
 
 module.exports = fake;