sinon-stub-promise
v4.0.0
Published
Synchronous Promise stubbing for Sinon.JS
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sinon-stub-promise
This is a little package that makes testing of promises easier when stubbing with Sinon.JS. This library ensures stubbed promises are evaluated synchronously, so that no special async tricks are required for testing.
Installation
Install with npm: npm install --save-dev sinon-stub-promise
In node, you can initialize with sinon:
var sinon = require('sinon');
var sinonStubPromise = require('sinon-stub-promise');
sinonStubPromise(sinon);
Or in the browser, you can just include
node_modules/sinon-stub-promise/index.js
(assumes sinon is available on
window object).
Example
// Code under test
function doSomethingWithAPromise(promise, object) {
promise()
.then(function(value) {
// resolves
object.resolved = value
})
.catch(function(value) {
// rejects
object.rejected = value
});
}
// Test
describe('stubbing a promise', function() {
var promise;
beforeEach(function() {
promise = sinon.stub().returnsPromise();
});
it('can resolve', function() {
promise.resolves('resolve value')
var testObject = {};
doSomethingWithAPromise(promise, testObject);
expect(testObject.resolved).to.eql('resolve value');
});
it('can reject', function() {
promise.rejects('reject value')
var testObject = {};
doSomethingWithAPromise(promise, testObject);
expect(testObject.rejected).to.eql('reject value');
});
}
Why?
We wanted a nice synchronous way of stubbing out promises while testing, and the existing solution, sinon-as-promised, uses a promise under the hood to achieve the stubbing. The issue with this, is that the promise is evaluated asynchronously, so the test code has to deal with that by delaying the assertion until the promise has a chance to run.
Additionally, sinon-as-promised requires you to call either stub.resolves()
or stub.rejects()
before it will setup the stub as a "thenable" object (one
that has then
and catch
on it). The trouble with this is that if you are
testing conditional branches (e.g. test what happens when promise succeeds,
then test what happens when promise fails), you have to either resolve or
reject the promise for the code under test to pass.
Usage with Karma
In order to use this with the Karma test runner
you can either add node_modules/sinon-stub-promise/index.js
to files
in your config or, alternatively, use the
karma-sinon-stub-promise plugin.
Stability?
This is not a Promises/A+ compliant library. We built it to support how we are currently using promises. There is a test suite that will grow over time as we identify any short comings of this library.
To Do
- Allow for chaining with
withArgs
. Ideally we could do things likesinon.stub().withArgs(42).resolves('value')
.