jest mocking functions without passing as a callback - node.js

Question

I have some code like:
module.exports = {
idCheck: function(errors) {
errors.some( (error) => {
if (error.parentSchema.regexp === '/^((?!\\bMyId\\b).)*$/i') {
this._recordError('IDCHECK');
}
});
}
};
I am trying to test it using jest with this:
const IDCheck = require(
'./IDCheck'
);
let errors = [
{
parentSchema: {
regexp: '/^((?!\\bMyId\\b).)*$/i'
}
}
];
describe('IDCheck', () => {
afterEach(() => {
jest.restoreAllMocks();
});
it('calls _recordError with IDCHECK', () => {
jest.spyOn(this, '_recordError');
IDCheck.idCheck(errors);
});
});
however, when running jest, I get
Cannot spy the _recordError property because it is not a function; undefined given instead
Is there a way of mocking, testing for _recordError() having been called, or not called and with the correct parameter, without passing _recordError through as a parameter?

Answer 1

A few things about this line: jest.spyOn(this, '_recordError');
this has to be IDCheck because there is no this in scope since you are using arrow functions that inherit this if previously set (which it isn't). You can console.log(this) right above the line to prove that point.
'_recordError' is not a method of IDCheck. spyOn checks the target's methods, not methods called within it. Now if _recordError is a method of IDCheck, then you should be ok.
Finally, you basically have to return the data you want in order to verify it. There's no real way to check what was passed unless you return it.
Here's a solution I came up with that does not include some fixes you'd have to implement to fix the potential workflow flaws.
const IDCheck = {
idCheck: function(errors) {
return errors.map(error => {
if (error.parentSchema.regexp === '/^((?!\\bMyId\\b).)*$/i') {
return this._recordError('IDCHECK')
}
})
},
_recordError: function(data) {
return data
}
}
let errors = [
{
parentSchema: {
regexp: '/^((?!\\bMyId\\b).)*$/i'
}
}
];
describe('IDCheck', () => {
afterEach(() => {
jest.restoreAllMocks();
});
it('calls _recordError with IDCHECK', () => {
const spy = jest.spyOn(IDCheck, '_recordError')
const check = IDCheck.idCheck(errors).includes('IDCHECK')
expect(spy).toHaveBeenCalled()
expect(check).toBe(true)
});
});