Niños
Simple stubbing/spying for AVA
Example
Setup
const test = require('ninos')(require('ava'));t.context.stub()
const EventEmitter = require('events');
test('EventEmitter', t => {
let e = new EventEmitter();
let s = t.context.stub();
e.on('event', s);
e.emit('event');
t.is(s.calls.length, 1);
e.emit('event', 'arg');
t.is(s.calls[1].arguments[0], 'arg');
});t.context.spy()
const api = require('./api');
test('api.getCurrentUser()', t => {
let s = t.context.spy(api, 'request', () => {
return Promise.resolve({ id: 42 });
});
await api.getCurrentUser();
t.deepEqual(s.calls[0].arguments[0], {
method: 'GET',
url: '/api/v1/user',
});
});Install
yarn add --dev ninosUsage
ninos()
This method setups the t.context.stub() and t.context.spy() functions. It
hooks into AVA to automatically restore spies after each test.
const test = require('ninos')(require('ava'));
t.context.stub()
Call this method to create a function that you can use in place of any other function (as a callback/etc).
test('example', t => {
let s = t.context.stub(); // [Function]
});On that function is a calls property which is an array of all the calls you
made.
let s = t.context.stub();
s.call('this', 'arg1', 'arg2');
t.deepEqual(s.calls, [
{ this: 'this', arguments: ['arg1', 'arg2'], return: undefined },
]);You can optional pass an inner function to be called inside the stub to customize its behavior.
let s = t.context.stub((...args) => {
return 'hello!';
});
s();
t.deepEqual(s.calls, [
{ ..., return: 'hello!' },
]);If you want to customize the behavior based on the current call you can use
s.calls.
let s = t.context.stub((...args) => {
if (s.calls.length === 0) return 'one';
if (s.calls.length === 1) return 'two';
if (s.calls.length === 2) return 'three';
throw new Error('too many calls!');
});
t.is(s(), 'one');
t.is(s(), 'two');
t.is(s(), 'three');
t.throws(() => s()); // Error: too many calls!
t.context.spy()
If you need to write tests against a method on an object, you should use a spy instead of a stub.
let method = () => 'hello from method';
let object = { method };
let s = t.context.spy(object, 'method');Just like stubs, spies have a calls property.
let s = t.context.spy(object, 'method');
object.method.call('this', 'arg1', 'arg2');
t.deepEqual(s.calls, [
{ this: 'this', arguments: ['arg1', 'arg2'], return: 'hello from method'; },
]);By default, spies will call the original function. If you want to customize the behavior you can pass your own inner function.
let s = t.context.spy(object, 'method', (...args) => {
return 'hello from spy'
});
object.method();
t.deepEqual(s.calls, [
{ ..., return: 'hello from spy' },
]);If you still want access to the original function you can find it on
s.original.
let s = t.context.spy(object, 'method', (...args) => {
return s.original(...args) + ' and hello from spy';
});
object.method();
t.deepEqual(s.calls, [
{ ..., return: 'hello from method and hello from spy' },
]);Spies will automatically be restored at the end of your test, but if you want to do it yourself:
let s = test.context.spy(object, 'method');
object.method = s.original;API
Here is the basic API interface:
type Call =
| { this: any, arguments: Array<any>, return: any }
| { this: any, arguments: Array<any>, throw: any }; // when an error was thrown
type Stub = Function & { calls: Array<Call> };
type Spy = Function & { calls: Array<Call>, original: Function };Design
Niños tries to keep things as miminal as possible. So it avoids APIs like:
let s = t.context.stub();
s.onCall(0).returns('ret1');
s.onCall(1).returns('ret2');And:
t.toHaveBeenCalledWith(s, 'arg1', 'arg2');Instead you should write tests like this:
test('example', t => {
let s = t.context.stub(() => {
if (s.calls.length === 0) return 'ret1';
if (s.calls.length === 1) return 'ret2';
});
t.deepEqual(s.calls[0], ['arg1', 'arg2']);
});This is ultimately more flexible and doesn't end up with dozens of weird one-off APIs for you to memorize.
If you prefer the former, Sinon is the library for you.
Note: This is part of a proposal to add stubs/spies to AVA itself
