How to mock an inner function in Sinon?

Suppose I have two functions, foo is called inside a bar. I have a Meteor app, so I decided to use meteor mocha package along with sinon and chai and not jest

foo

bar

mocha

sinon

chai

jest

// foo.js

const foo = () => // call to a google maps api;
export default foo;


// bar.js

const bar = (x) =>
foo();
...
;
export default bar;


What is the correct approach of mocking foo in this case

foo

Currently I've came up with the following solution:

import foo from 'path/to/foo.js'
import bar from 'path/to/bar.js'

describe('my test suite', function()
it('should pass the test', function()
foo = spy();
bar(5);
assert(foo.calledOnce);
);
);


The following code works, but is that correct to redefine foo?

foo

UPDATE

Also, it's not possible to create a mock or stub this way, which makes me think that Sinon is not suitable for mocking standalone functions

1 Answer
1

Sinon works well on standalone JavaScript functions.

Sinon

Here is an example of how to wrap the default export of a module in a Sinon spy:

Sinon

import * as sinon from 'sinon';
import * as fooModule from 'path/to/foo.js'
import bar from 'path/to/bar.js'

describe('my test suite', function()
it('should pass the test', function()
const spy = sinon.spy(fooModule, 'default'); // wrap the function in a spy
bar(5);
assert(spy.calledOnce); // SUCCESS
spy.restore(); // restore the original function
);
);


Here is an example of how to replace the default export of a module with a Sinon stub:

Sinon

import * as sinon from 'sinon';
import * as fooModule from 'path/to/foo.js'
import bar from 'path/to/bar.js'

describe('my test suite', function()
it('should pass the test', function()
const stub = sinon.stub(fooModule, 'default').returns('something else'); // stub the function
bar(5); // foo() returns 'something else' within bar(5)
assert(stub.calledOnce); // SUCCESS
stub.restore(); // restore the original function
);
);


assert(stub.called);

spy

stub

restore

notCalled:true

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