How Do I Test Call And Apply Functions In Jest?

Here's my callnapply.js file const callAndApply = { caller(object, method, nameArg, ageArg, tShirtSizeArg) { method.call(object, nameArg, ageArg, tShirtSizeArg); }, appli

Solution 1:

You can mock the .call() method itself:

const outer = function() {}
outer.call = jest.fn()

Then you can do usual jest mock tests on outer.call.

Here is the working test file:

const callnapply = require('./callnapply');

test('testing Function.prototype.call as mock function', () => {
    const outer = function() {};
    outer.call = jest.fn();
    const name = 'Aakash';
    const age = 22;
    const tee = 'M';
    callnapply.caller(this, outer, name, age, tee);
    expect(outer.call).toHaveBeenCalledWith(this, name, age, tee);
});

See this working REPL.