When

Stubbing library for chained SDKs.

• Pass in a real instance.
• Every function call gets a new stub, mapped by arguments.
• Last function or property can either thenReturn or thenCall.

I needed some way to test pnpjs, and this library in combination with ava and rewiremock works great.

Install

npm i @eirikb/when

Example

const when = require('@eirikb/when');

const greet = {
  hello() {
    console.log('hello called');
    return {
      world() {
        console.log('world called');
        return 'Hello, world!';
      },
    };
  },
};

const stub = when(greet);
// Print "hello called"
stub.hello().world.thenReturn('Oh no!');

// Print "hello called"
t.is('Oh no!', stub.hello().world());

stub.hello.thenCall(() => {
  console.log('Called');
  t.pass();
});

// Print "called"
stub.hello();

Example Azure Function-ish setup

index.js

const { sp } = require('@pnp/sp-commonjs');

module.exports = async () => {
  const spItem = sp.web.getList('web/Lists/A').items.getById(137);
  const item = await spItem.get();

  await spItem.update({
    Sum: item.Sum + 100,
  });
};

test.js

const test = require('ava');
const rewiremock = require('rewiremock/node');
const { sp } = require('@pnp/sp-commonjs');
const when = require('@eirikb/when');

const spStub = when(sp);
rewiremock('@pnp/sp-commonjs').with({ sp: spStub });
rewiremock.enable();

test('Sum', async t => {
  t.plan(1);
  const spItem = sp.web.getList('web/Lists/A').items.getById(137);
  spItem.get.thenReturn({ Sum: 600 });
  spItem.update.thenCall(item => {
    t.deepEqual({ Sum: 700 }, item);
  });

  await require('./index')();
});

TypeScript

If you use TypeScript the thenCall and thenReturn will give you errors, to solve this you can import when as { when } and use this.
Default export you can rename as something else, e.g., initWhen.

Example:

import initWhen, { when } from '@eirikb/when';

const greet = {
  hello() {
    console.log('hello called');
    return {
      world() {
        console.log('world called');
        return 'Hello, world!';
      },
    };
  },
};

const stub = initWhen(greet);
// Print "hello called"
when(stub.hello().world).thenReturn('Oh no!');

// Print "hello called"
t.is('Oh no!', stub.hello().world());

when(stub.hello).thenCall(() => {
  console.log('Called');
  t.pass();
});

// Print "called"
stub.hello();