I am running some tests using Jest. I have defined some variables. Some tests will modify the variables, for example, adding an item to an array. After each test, I want to variables to reset to the values that they were originally assigned to, so each test has the original data to work with. Is this possible? Does Jest have a solution to this?

For example

import * as matchers from "jest-extended";
expect.extend(matchers);

const array = [1, 2, 3];

const addFour = array => array.push(4);

const addFive = array => array.push(5);

describe("tests", () => {
  it("should add 4 to the array", () => {
    addFour(array);
    expect(array).toHaveLength(4);
  });

  //array should be [1, 2, 3, 4]

  it("should add 5 to the array", () => {
    addFive(array);
    expect(array).toHaveLength(4);
  });
  //array should be [1, 2, 3, 5] and not [1, 2, 3, 4, 5]
});

I have edited the problem to better resemble my test case. The issue has been resolved. Please see below.

CodePudding user response：

You could use the beforeEach function of Jest to initialize the variable.

let array;

beforeEach(() => {
    array = [1, 2, 3];
});

However in your example the addFour and addFive methods are non-mutating, meaning they won't change the value of the array variable. In this case there's no need to reset the value of the array because it never changes.