added __with__ function according to proposed syntax in issue #29

1 files changed, 77 insertions, 1 deletions

diff --git a/test/__set__.test.js b/test/__set__.test.js
index ff1a3d2..fe6f529 100644
--- a/test/__set__.test.js
+++ b/test/__set__.test.js
@@ -1,5 +1,7 @@
 var expect = require("expect.js"),
-    __set__ = require("../lib/__set__.js"),
+    setModule = require("../lib/__set__.js")
+    __set__ = setModule["__set__"],
+    __with__ = setModule["__with__"],
     vm = require("vm"),
 
     expectReferenceError = expectError(ReferenceError),
@@ -125,3 +127,77 @@ describe("__set__", function () {
         }).to.throwException(expectTypeError);
     });
 });
+
+describe("__with__", function() {
+    var moduleFake;
+
+    beforeEach(function () {
+        moduleFake = {
+            myValue: 0,    // copy by value
+            myReference: {}       // copy by reference
+        };
+
+        //__with__ requires __set__ to be in scope
+        vm.runInNewContext(
+            "__set__ = " + __set__.toString() + "; " +
+            "__with__ = " + __with__.toString() + "; " +
+            "getValue = function () { return myValue; }; " +
+            "getReference = function () { return myReference; }; ",
+            moduleFake
+        );
+    });
+
+    it("should return a function that can be invoked with a callback which guarantees __sets__ undo function is called for you at the end", function () {
+        var newObj = { hello: "hello" };
+
+        expect(moduleFake.getValue()).to.be(0);
+        expect(moduleFake.getReference()).to.eql({});
+
+        moduleFake.__with__({
+            myValue: 2,
+            myReference: newObj
+        })(function() {
+          //changes will be visible from within this callback function
+          expect(moduleFake.getValue()).to.be(2);
+          expect(moduleFake.getReference()).to.be(newObj);
+        })
+
+        //undo will automatically get called for you after returning from your callback function
+        expect(moduleFake.getValue()).to.be(0);
+        expect(moduleFake.getReference()).to.eql({});
+    });
+
+    it("should still revert values if the callback throws an exception", function(){
+        var newObj = { hello: "hello" };
+        function withError(){
+          moduleFake.__with__({
+              myValue: 2,
+              myReference: newObj
+          })(function() {
+            throw new Error("something went wrong...");
+          })
+        }
+        expect(withError).to.throwError();
+        expect(moduleFake.getValue()).to.be(0);
+        expect(moduleFake.getReference()).to.eql({});
+    });
+
+    it("should throw an error if something other than a function is passed as the callback", function() {
+        var newObj = { hello: "hello" },
+            withFunction = moduleFake.__with__({
+                myValue: 2,
+                myReference: newObj
+            })
+            callWithFunction = function(){
+              var args = arguments;
+              return function() {
+                withFunction.apply(null, args);
+              };
+            };
+
+        expect(callWithFunction(1)).to.throwError();
+        expect(callWithFunction("a string")).to.throwError();
+        expect(callWithFunction({})).to.throwError();
+        expect(callWithFunction(function(){})).to.not.throwError();
+    });
+});