Nano Spy
A tiny Node.js library to spy and mock methods in tests with great TypeScript support.
It will take only 5 KB
in your node_modules and have 0 dependencies.
import { spyOn, restoreAll } from 'nanospy'
test.after.each(() => {
restoreAll()
})
test('calls increase', () => {
const spy = spyOn(counter, 'increase')
counter.increase(5)
assert.equal(spy.callCount, 1)
assert.equal(spy.calls, [[5]])
})
Usage
Method Spy
Spy tracks method calls, but do not change method’s behavior.
import { spyOn, restoreAll } from 'nanospy'
test.after.each(() => {
restoreAll()
})
test('calls increase', () => {
const spy = spyOn(counter, 'increase')
counter.increase(5)
assert.is(spy.called, true)
assert.equal(spy.callCount, 1)
assert.equal(spy.calls, [[5]])
assert.equal(spy.results, [true])
})Mock
Mock change the method’s behavior.
const spy = spyOn(global, 'fetch', async () => {
return {
json: () => ({ posts })
}
})Or change next function call:
spy.nextResult({ ok: false })spy.nextError(error)Functions
spy can be used to track callback calls.
import { spy } from 'nanospy'
const fn = spy()
fn('a', 10)
fn.callCount //=> 1
fn.calls //=> [['a', 10]]You can pass spy’s callback:
let fn = spy((name: string) => {
console.log(`Hello, ${name}!`)
})
fn('Ivan') //=> Hello, Ivan!Or change next function call:
fn.nextResult({ ok: false })fn.nextError(error)Remocking
You can reassign mocked function with onCall method:
const obj = {
mark: str => str + '!',
}
const spy = spyOn(obj, 'mark')
obj.mark('a')
assert.equal(spy.results, ['a!'])
spy.onCall(str => str + '?')
obj.mark('a')
assert.equal(spy.results, ['a!', 'a?'])