clear encapsulated value in imported module – Jest js

January 14, 2022

Let’s say I’m importing to Jest module like:

let var;

export const getVar = () => {
    if(var == null) {
        var =  Date.now()
    }

    return var;
}

I am trying to make unit tests for this module, however, on every unit test I have to reset the "var" value. I’ve tried to redefine the module using require on "beforeEach" method but it does not work. Does anyone know how to reset encapsulated values like this?

>Solution :

Using old `require` syntax and `resetModules`

foo.js

let foo;

const getFoo = () => {
  if (!foo) {
    foo = "foo";
  } else {
    foo = "bar";
  }
  return foo;
};

module.exports = { getFoo };

foo.test.js

beforeEach(() => jest.resetModules());

test("first", () => {
  const { getFoo } = require("./foo");
  expect(getFoo()).toBe("foo");
});

test("second", () => {
  const { getFoo } = require("./foo");
  expect(getFoo()).toBe("foo");
});

Using dynamic `import` and `resetModules`

foo.js

let foo;

export const getFoo = () => {
  if (!foo) {
    foo = "foo";
  } else {
    foo = "bar";
  }
  return foo;
};

foo.test.js

import { jest } from "@jest/globals";
let getFoo;

beforeEach(async () => {
  jest.resetModules();
  const { getFoo: getFooAlias } = await import("./foo.js");
  getFoo = getFooAlias;
});

test("first", () => {
  expect(getFoo()).toBe("foo");
});

test("second", () => {
  expect(getFoo()).toBe("foo");
});