install and use any-promise (#504)

* export a use function from lib/promises

closes #478

the `use` function can be used to change the promise implementation
that is used by the library

Author: gurpreetatwal

lib/promises.js

@@ -1,10 +1,12 @@
 'use strict';
 
+var Promise = global.Promise;
+
 /// encapsulate a method with a node-style callback in a Promise
 /// @param {object} 'this' of the encapsulated function
 /// @param {function} function to be encapsulated
 /// @param {Array-like} args to be passed to the called function
-/// @return {Promise} a Promise encapuslaing the function
+/// @return {Promise} a Promise encapsulating the function
 module.exports.promise = function (fn, context, args) {
 
     if (!Array.isArray(args)) {
@@ -32,3 +34,9 @@ module.exports.promise = function (fn, context, args) {
 module.exports.reject = function (err) {
     return Promise.reject(err);
 };
+
+/// changes the promise implementation that bcrypt uses
+/// @param {Promise} the implementation to use
+module.exports.use = function(promise) {
+  Promise = promise;
+};

test/promise.js

@@ -1,4 +1,5 @@
 var bcrypt = require('../bcrypt');
+var promises = require('../lib/promises');
 
 var fail = function(assert, error) {
     assert.ok(false, error);
@@ -215,6 +216,37 @@ if (typeof Promise !== 'undefined') {
             }).then(function() {
                 assert.done();
             });
+        },
+        test_change_promise_impl_reject: function(assert) {
+
+          promises.use({
+            reject: function() {
+              return 'mock';
+            }
+          });
+
+          assert.equal(promises.reject(), 'mock');
+
+          // need to reset the promise implementation because of require cache
+          promises.use(global.Promise);
+          assert.done();
+
+        },
+        test_change_promise_impl_promise: function(assert) {
+
+          promises.use({
+            reject: function(err) {
+              assert.equal(err.message, 'fn must be a function');
+              return 'mock';
+            }
+          });
+
+          assert.equal(promises.promise('', '', ''), 'mock');
+
+          // need to reset the promise implementation because of require cache
+          promises.use(global.Promise);
+          assert.done();
+
         }
     };
 }