FinishedPromise.install() replaces native Promise

README.md

@@ -32,3 +32,15 @@ describe('FinishedPromise', () => {
   })
 })
 ```
+
+## async / await
+
+Overriding `global.Promise` has no effect on `async` functions - they will use
+the native v8 `Promise` regardless.
+
+To circumvent this limitation we can transpile the source code prior to running
+it. Babel can do this, although rather slowly, which would defeat the purpose
+of this library - fast tests!
+
+Instead we can use [async-to-gen](https://github.com/leebyron/async-to-gen) which
+is actually very fast. See `./mocha` for an example.

index.js

@@ -100,4 +100,14 @@ FinishedPromise.reject = function(error) {
   })
 }
 
+const nativePromise = Promise
+
+FinishedPromise.install = function() {
+  Promise = FinishedPromise
+}
+
+FinishedPromise.uninstall = function() {
+  Promise = nativePromise
+}
+
 module.exports = FinishedPromise

mocha

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+node_modules/.bin/async-node node_modules/.bin/_mocha "$@"

package.json

@@ -4,11 +4,12 @@
   "description": "Synchronous implementation of Promise for use in tests",
   "main": "index.js",
   "scripts": {
-    "test": "./node_modules/.bin/mocha"
+    "test": "./mocha"
   },
   "author": "Josh Chisholm <joshuachisholm@gmail.com>",
   "license": "MIT",
   "devDependencies": {
+    "async-to-gen": "^1.3.3",
     "mocha": "^3.2.0"
   },
   "repository": {

test/_globalPromiseTest.js

@@ -0,0 +1,40 @@
+const assert = require('assert')
+const FinishedPromise = require('..')
+
+describe('Promise', () => {
+  before(() => {
+    FinishedPromise.install()
+  })
+
+  after(() => {
+    FinishedPromise.uninstall()
+  })
+
+  it('is replaced with FinishedPromise', () => {
+    let result
+
+    function f1(v) {
+      return Promise.resolve(v)
+    }
+    function f2(v) {
+      result = v
+    }
+
+    Promise.resolve(123).then(f1).then(f2)
+    assert.equal(result, 123)
+  })
+
+  it('is replaced with FinishedPromise in async functions', () => {
+    let result
+
+    async function f1(v) {
+      return v
+    }
+    async function f2(v) {
+      result = v
+    }
+
+    Promise.resolve(123).then(f1).then(f2)
+    assert.equal(result, 123)
+  })
+})