Make sandboxes each use their own assert object

lib/sinon/assert.js

@@ -15,6 +15,7 @@ var forEach = arrayProto.forEach;
 var join = arrayProto.join;
 var splice = arrayProto.splice;
 
+function createAssertObject() {
     var assert;
 
     function verifyIsStub() {
@@ -97,7 +98,9 @@ function mirrorPropAsAssertion(name, method, message) {
     }
 
     function exposedName(prefix, prop) {
-    return !prefix || /^fail/.test(prop) ? prop : prefix + stringSlice(prop, 0, 1).toUpperCase() + stringSlice(prop, 1);
+        return !prefix || /^fail/.test(prop)
+            ? prop
+            : prefix + stringSlice(prop, 0, 1).toUpperCase() + stringSlice(prop, 1);
     }
 
     assert = {
@@ -214,4 +217,8 @@ mirrorPropAsAssertion("neverCalledWithMatch", "expected %n to never be called wi
     mirrorPropAsAssertion("threw", "%n did not throw exception%C");
     mirrorPropAsAssertion("alwaysThrew", "%n did not always throw exception%C");
 
-module.exports = assert;
+    return assert;
+}
+
+module.exports = createAssertObject();
+module.exports.createAssertObject = createAssertObject;

lib/sinon/sandbox.js

@@ -37,6 +37,8 @@ function Sandbox() {
     var fakeRestorers = [];
     var promiseLib;
 
+    sandbox.assert = sinonAssert.createAssertObject();
+
     sandbox.serverPrototype = fakeServer;
 
     // this is for testing only
@@ -410,7 +412,6 @@ function Sandbox() {
     };
 }
 
-Sandbox.prototype.assert = sinonAssert;
 Sandbox.prototype.match = match;
 
 module.exports = Sandbox;

test/sandbox-test.js

@@ -15,7 +15,6 @@ var sinonFake = require("../lib/sinon/fake");
 var sinonSpy = require("../lib/sinon/spy");
 var sinonStub = require("../lib/sinon/stub");
 var sinonConfig = require("../lib/sinon/util/core/get-config");
-var sinonAssert = require("../lib/sinon/assert");
 var sinonClock = require("../lib/sinon/util/fake-timers");
 
 var supportsAjax = typeof XMLHttpRequest !== "undefined" || typeof ActiveXObject !== "undefined";
@@ -47,12 +46,6 @@ describe("Sandbox", function() {
         assert.same(sandbox.match, match);
     });
 
-    it("exposes assert", function() {
-        var sandbox = new Sandbox();
-
-        assert.same(sandbox.assert, sinonAssert);
-    });
-
     it("can be reset without failing when pre-configured to use a fake server", function() {
         var sandbox = createSandbox({ useFakeServer: true });
         refute.exception(function() {
@@ -2077,4 +2070,31 @@ describe("Sandbox", function() {
             assert.equals(object.prop, "bla");
         });
     });
+
+    describe(".assert", function() {
+        it("allows rebinding of .fail on a per-sandbox level", function() {
+            var sandboxA = createSandbox();
+            var sandboxB = createSandbox();
+
+            sandboxA.assert.failException = "CustomErrorA";
+            sandboxB.assert.failException = "CustomErrorB";
+
+            assert.exception(
+                function() {
+                    sandboxA.assert.fail("Some message");
+                },
+                { name: "CustomErrorA" }
+            );
+
+            assert.exception(
+                function() {
+                    sandboxB.assert.fail("Some message");
+                },
+                { name: "CustomErrorB" }
+            );
+
+            sandboxA.restore();
+            sandboxB.restore();
+        });
+    });
 });