How check if static methods is called in Jest?

user_11026537 0
Viewed 569

I have ES-6 class which is having static methods. How to mock them in Jest to test if they gets called?

I have 3 files

  1. Logger
class Logger {
  static log = (err) => {
    console.log(err);
  }
}
export default Logger;
  1. action
// import Logger './Logger';
export const myAction = () => {
  handleRequest(params).then((response) => {
    // Statements
  }).catch((err) => {
    Logger.log(err);
  });
};
  1. Test file
// import {myAction} from './action';
// import Logger './Logger';
it('should call Logger', () => {
  Logger.log = jest.fn();
  return myAction().then(() => {
    expect(Logger.log).toHaveBeenCalled(); // It is failing
  });
});
enzyme jestjs ecmascript-6 javascript
2 Answers

You can use jest.spyOn(object, methodName)

import Logger './Logger';
import {myAction} from './action';

it('should call Logger', async () => {
  const spy = jest.spyOn(Logger, "log");
  await myAction();
  expect(spy).toHaveBeenCalled();
});

or

import Logger './Logger';
import {myAction} from './action';

it('should call Logger', () => {
  const spy = jest.spyOn(Logger, "log");
  return myAction().finally(() => {
    expect(spy).toHaveBeenCalled();
  });
});
user_143498080

You could just modify the class before creating the instance.

const foo = jest.fn()
const bar = jest.fn()

MyClass.foo = foo
MyClass.bar = bar

const myClass = new MyClass()

myClass.foo()

expect(foo).toHaveBeenCalled()

If this is the right approach depends on the way to are testing MyClass

edit: I honestly think @lissettdm answer is a better way of doing it

user_68229620
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