babel-jest-assertions
Adds expect.assertions(n) and expect.hasAssertions to all tests automatically
Problem
Ever wondered if your tests are actually running their assertions, especially in asynchronous tests? Jest has two features
built in to help with this: expect.assertions(number)
and expect.hasAssertions(). These can be
useful when doing something like:
it('resolves to one', () => {
Promise.reject(1).then(value => expect(value).toBe(1));
});The issue here is the catch case is not dealt with in this test, which is fine as we are testing the happy path,
but this test will currently pass even though the Promise rejects and the assertion is never ran.
Solution
One solution is to manually adjust the above test to include expect.assertions(number) and expect.hasAssertions()
this is quite verbose and prone to human error.
An alternative is a babel plugin to automate adding these additional properties, and this is such plugin
Installation
With npm:
npm install --save-dev babel-jest-assertionsWith yarn:
yarn add -D babel-jest-assertionsSetup
.babelrc
{
"plugins": ["babel-jest-assertions"]
}CLI
babel --plugins babel-jest-assertions script.jsNode
require('babel-core').transform('code', {
plugins: ['babel-jest-assertions'],
})Usage
Simply write your tests as you would normally and this plugin will add the verification of assertions in the background.
One assertion
it('resolves to one', () => {
Promise.reject(1).then(value => expect(value).toBe(1));
});↓ ↓ ↓ ↓ ↓ ↓
it('resolves to one', () => {
expect.hasAssertions();
expect.assertions(1);
Promise.reject(1).then(value => expect(value).toBe(1));
});Note: this test will now fail
Multiple assertions
it('counts multiple assertions too', () => {
expect(1 + 0).toBe(1);
expect(0 + 1).toBe(1);
});↓ ↓ ↓ ↓ ↓ ↓
it('counts multiple assertions too', () => {
expect.hasAssertions();
expect.assertions(2);
expect(1 + 0).toBe(1);
expect(0 + 1).toBe(1);
});Asynchronous assertions
it('counts multiple assertions too', async () => {
const res = await fetch('www.example.com');
expect(res.json).toBeTruthy();
const json = await res.json();
expect(json).toEqual({ whatever: 'trevor' });
});↓ ↓ ↓ ↓ ↓ ↓
it('counts multiple assertions too', async () => {
expect.hasAssertions();
expect.assertions(2);
const res = await fetch('www.example.com');
expect(res.json).toBeTruthy();
const json = await res.json();
expect(json).toEqual({ whatever: 'trevor' });
});beforeEach and afterEach blocks
If you have expectations inside either of beforeEach or afterEach blocks for your test then these expects will be
included in the count - even if you have nested describe blocks each with their own beforeEach/afterEach the count
will accumulate.
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
describe('.add', () => {
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
it('returns 1 when given 0 and 1', () => {
expect(add(1, 0)).toEqual(1);
});
describe('.add2', () => {
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
it('returns 1 when given 0 and 1', () => {
expect(add2(1, 0)).toEqual(1);
});
});
});
↓ ↓ ↓ ↓ ↓ ↓
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
describe('.add', () => {
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
it('returns 1 when given 0 and 1', () => {
expect.assertions(5);
expect.hasAssertions();
expect(add2(1, 0)).toEqual(1);
});
describe('.add2', () => {
beforeEach(() => {
expect(true).toBe(true);
});
afterEach(() => {
expect(true).toBe(true);
});
it('returns 1 when given 0 and 1', () => {
expect.assertions(7);
expect.hasAssertions();
expect(add2(1, 0)).toEqual(1);
});
});
});Comments are ignored
it('ignores commented-out assertions', async () => {
const res = await fetch('www.example.com');
// expect(res.json).toBeTruthy();
const json = await res.json();
/*
expect(json).toEqual({ whatever: 'trevor1' });
*/
expect(json).toEqual({ whatever: 'trevor' });
/* expect(json).toEqual({ whatever: 'trevor2' }); */
});↓ ↓ ↓ ↓ ↓ ↓
it('counts multiple assertions too', async () => {
expect.hasAssertions();
expect.assertions(1);
const res = await fetch('www.example.com');
// expect(res.json).toBeTruthy();
const json = await res.json();
/*
expect(json).toEqual({ whatever: 'trevor1' });
*/
expect(json).toEqual({ whatever: 'trevor' });
/* expect(json).toEqual({ whatever: 'trevor2' }); */
});Override
If you add either expect.assertions(number) or expect.hasAssertions() then your defaults will be favoured and the
plugin will skip the test.
it('will leave test as override supplied', () => {
expect.hasAssertions();
expect.assertions(1);
if (true) {
expect(true).toBe(true);
}
if (false) {
expect(false).toBe(false);
}
});↓ ↓ ↓ ↓ ↓ ↓
it('will leave test as override supplied', () => {
expect.hasAssertions();
expect.assertions(1);
if (true) {
expect(true).toBe(true);
}
if (false) {
expect(false).toBe(false);
}
});Contributors
 Matt Phillips |
 Ramesh Nair |
 Huy Nguyen |
 Simon Boudrias |
 Giuseppe |
|---|
LICENSE
MIT
