How to Use Mocks with Sinon

Feb 4, 2022

Mocks allow you to create a fake function that passes or fails depending on your needs. You can ensure it was called with certain arguments, or check how many times it was called. You must call mock() on an object. To complete the test, you must call the verify() function to check that all the mock's expectations were met.

const sinon = require('sinon');
const obj = {
  method: function() {
    console.log('Hello World')
  }
};
const mock = sinon.mock(obj);
mock.expects('method').once();

// 'Hello World' will not print since 'method' is stubbed out
obj.method();

// Succeeds
mock.verify();

using verify()

The verify() function will throw an error if the expectations are not met, or return true otherwise. You must define the expectations before calling verify().

const sinon = require('sinon');
const obj = {
  method: function() {
    console.log('Hello World');
  }
};
const mock = sinon.mock(obj);
mock.expects('method').once();
obj.method();
mock.verify(); // true

using mock.restore()

The restore() function returns the mocked functions back to their original state, meaning that they will now execute whatever lines of code you had written.

const sinon = require('sinon');
const obj = {
  method: function() {
    console.log('Hello World');
  }
};
const mock = sinon.mock(obj);
mock.expects('method').once();
obj.method();
mock.verify(); // true

mock.restore();
obj.method(); // Hello World

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