Avoid mutating the global Promise

src/environment.js

@@ -18,9 +18,12 @@ function toFastProperties(obj) {
   (function () {}).prototype = obj;
 }
 
-Object.keys(Promise.prototype).filter(isNotMethod).forEach(del(Promise.prototype));
-Object.keys(Promise).filter(isNotMethod).forEach(del(Promise));
-toFastProperties(Promise);
-toFastProperties(Promise.prototype);
+const PromiseCopy = Object.assign({}, Promise);
+PromiseCopy.prototype = Object.assign({}, Promise.prototype);
 
-global.Promise = Promise;
+Object.keys(Promise.prototype).filter(isNotMethod).forEach(del(PromiseCopy.prototype));
+Object.keys(Promise).filter(isNotMethod).forEach(del(PromiseCopy));
+toFastProperties(PromiseCopy);
+toFastProperties(PromiseCopy.prototype);
+
+global.Promise = PromiseCopy;

test/environment-test.js

@@ -0,0 +1,30 @@
+import { assert } from 'chai';
+import Promise from 'bluebird';
+import '../src/environment';
+
+
+describe('environment', () => {
+  it('does not modify the Promise package', () => {
+    assert.notStrictEqual(Promise, global.Promise);
+  });
+
+  describe('global promise', () => {
+    it('has ES6 methods', () => {
+      assert.isFunction(global.Promise.prototype.then);
+      assert.isFunction(global.Promise.prototype.catch);
+      assert.isFunction(global.Promise.prototype.constructor);
+    });
+
+    it('has ES6 static methods', () => {
+      assert.isFunction(global.Promise.all);
+      assert.isFunction(global.Promise.race);
+      assert.isFunction(global.Promise.resolve);
+      assert.isFunction(global.Promise.reject);
+      assert.isFunction(global.Promise.cast);
+    });
+
+    it('removes extraneous methods', () => {
+      assert.isUndefined(global.Promise.promisifyAll);
+    });
+  });
+});