How to preserve localStorage between Cypress tests
Tags: cypress, testing, localstorage, javascript
Published: 2021-04-20 04:58:00

Cypress by default clears localStorage between tests, which may be a problem when you are trying to test features related to it. But there is a Cypress plugin that allows preserving localStorage between tests and disabling localStorage.

## The problems

* You want to preserve localStorage between Cypress tests.
* You want to preserve localStorage between Cypress spec files.
* You want to disable localStorage to check error handling.

## The solution

The [`cypress-localstorage-commands` plugin](https://github.com/javierbrea/cypress-localstorage-commands) allows you to use all browser localStorage methods through Cypress commands, and preserve it between tests and spec files. It also allows to simulate that localStorage is disabled in the browser.

## Alternatives

As from Cypress 12, you can use cy.session and Cypress Test Isolation in order to persist localStorage between tests. Anyway, the plugin can be still used for an easier manipulation of the localStorage, writing localStorage assertions and even [disabling it for checking the error handling](https://dev.to/javierbrea/testing-localstorage-exceptions-with-cypress-93n).

## Installation

The module is distributed via npm which is bundled with node and should be installed as one of your project's devDependencies:

```bash
npm i --save-dev cypress-localstorage-commands
```

### Installing commands

`cypress-localstorage-commands` extends Cypress' cy commands.

At the top of your Cypress' support file (usually `cypress/support/e2e.js` for `e2e` testing type):

```javascript
import "cypress-localstorage-commands";
```

Read [Cypress configuration docs](https://docs.cypress.io/guides/references/configuration) for further info.

### Installing Node events

__⚠ In order to support preserving localStorage across Cypress spec files, the plugin's Node events must be installed also.__ Otherwise, localStorage will be preserved only across tests in the same spec file.

In the `cypress.config.js` file:

```javascript
module.exports = {
  e2e: {
    setupNodeEvents(on, config) {
      require("cypress-localstorage-commands/plugin")(on, config);
      return config;
    },
  },
};
```

## Usage

### Commands

#### `cy.saveLocalStorage()`

Saves current localStorage values into an internal "snapshot".

#### `cy.restoreLocalStorage()`

Restores localStorage to previously "snapshot" saved values.

#### `cy.clearLocalStorageSnapshot()`

Clears localStorage "snapshot" values, so previously saved values are cleaned.

#### `cy.getLocalStorage(item)`

Gets localStorage item. Equivalent to `localStorage.getItem` in browser.

* `item` _(String)_: Item to get from `localStorage`.

#### `cy.setLocalStorage(item, value)`

Sets localStorage item. Equivalent to `localStorage.setItem` in browser.

* `item` _(String)_: Item to set value.
* `value` _(String)_: Value to be set.

#### `cy.removeLocalStorage(item)`

Removes localStorage item. Equivalent to `localStorage.removeItem` in browser.

* `item` _(String)_: Item to be removed.

#### `cy.disableLocalStorage(options)`

Disables localStorage. It produces localStorage methods to throw errors.

* `options` _(Object)_: Options to use when disabling `localStorage`.
  * `withError` _(Error)_: If provided, invocations to `localStorage` methods will throw this error.

### Preserving local storage between tests

Use `cy.saveLocalStorage()` to save a snapshot of current `localStorage` at the end of one test, and use the `cy.restoreLocalStorage()` command to restore it at the beginning of another one. _The usage of `beforeEach` and `afterEach` is recommended for this purpose._

> ⚠ When the [plugin's Node events are installed](#installing-node-events), the `cy.restoreLocalStorage()` command will be able to restore the localStorage snapshots saved in other spec files. Otherwise, snapshots are completely cleared between spec files.

### Examples

#### Cookies button example

Next example shows how the plugin can be used to test a "cookies button" _(which theorically sets a flag into `localStorage` and can be clicked only once)_

```js
describe("Accept cookies button", () => {
  const COOKIES_BUTTON = "#accept-cookies";

  before(() => {
    cy.clearLocalStorageSnapshot();
  });

  beforeEach(() => {
    cy.restoreLocalStorage();
    cy.visit("/");
  });

  afterEach(() => {
    cy.saveLocalStorage();
  });

  it("should be visible", () => {
    cy.get(COOKIES_BUTTON).should("be.visible");
  });

  it("should not be visible after clicked", () => {
    cy.get(COOKIES_BUTTON).click();
    cy.get(COOKIES_BUTTON).should("not.be.visible");
  });

  it("should not be visible after reloading", () => {
    cy.get(COOKIES_BUTTON).should("not.be.visible");
  });
});
```

> Note the usage of `beforeEach` and `afterEach` for preserving `localStorage` between all tests. Also `cy.clearLocalStorageSnapshot` is used in the `before` statement to avoid possible conflicts with other spec files preserving localStorage.

#### localStorage assertions

Based on the previous example, assertions could be added to check values of `localStorage`:

```js
describe("localStorage cookies-accepted item", () => {
  beforeEach(() => {
    cy.restoreLocalStorage();
    cy.visit("/");
  });

  afterEach(() => {
    cy.saveLocalStorage();
  });

  it("should be null first time page is visited", () => {
    cy.getLocalStorage("cookies-accepted").should("equal", null);
  });

  it("should be true after clicking cookies button", () => {
    cy.get("#accept-cookies").click();
    cy.getLocalStorage("cookies-accepted").should("equal", "true");
  });

  it("should be true after reloading", () => {
    cy.getLocalStorage("cookies-accepted").then(cookiesAccepted => {
      expect(cookiesAccepted).to.equal("true");
    });
  });
});
```

### Disabling localStorage

Use `cy.disableLocalStorage()` to simulate that `localStorage` is disabled, producing that any invocation to `localStorage.setItem`, `localStorage.getItem`, `localStorage.removeItem` or `localStorage.clear` will throw an error. [As MDN docs recommend](https://developer.mozilla.org/en-US/docs/Web/API/Storage/setItem), _"developers should make sure to always catch possible exceptions from setItem()"_. This command allows to test that possible exceptions are handled correctly.

Note that:

* Only pages loaded after calling this command will have `localStorage` disabled, so always use `cy.reload` or `cy.visit` after executing it.
* The `localStorage` only remains disabled for all pages loaded during the current test. If you want to disable it for multiple tests, execute it in all of them, or in a `beforeEach` statement.
* If any of the other plugin commands (except `clearLocalStorageSnapshot`) is executed while `localStorage` is disabled, it will do nothing but producing a Cypress log as: _"localStorage.setItem is disabled"_

### Examples

#### Disabling localStorage in a single test

Based on previous "Accept cookies button" example, next tests could be added:

```js
//...
const LOCALSTORAGE_DISABLED_WARNING = "#localstorage-disabled-warning";
const LOCALSTORAGE_ERROR = "#localstorage-error";

//... should not be visible after clicked

it("should still be visible when reloading if localStorage is disabled", () => {
  cy.disableLocalStorage();
  cy.reload();
  cy.get(COOKIES_BUTTON).should("be.visible");
});

it("should display warning if localStorage is disabled", () => {
  cy.disableLocalStorage();
  cy.reload();
  cy.get(LOCALSTORAGE_DISABLED_WARNING).should("be.visible");
});

it("should display localStorage error message", () => {
  cy.disableLocalStorage();
  cy.reload();
  cy.get(LOCALSTORAGE_ERROR).should("have.text", "Error");
});

// ...should not be visible after reloading
```

#### Disabling localStorage in multiple tests

```js
describe("when localStorage is disabled", () => {
  beforeEach(() => {
    cy.disableLocalStorage({
      withError: new Error("Disabled by cypress-localstorage-commands"),
    });
    cy.visit("/");
  });

  it("should display localStorage warning", () => {
    cy.get("#localstorage-disabled-warning").should("be.visible");
  });

  it("should display localStorage error message", () => {
    cy.get("#localstorage-error").should("have.text", "Disabled by cypress-localstorage-commands");
  });

  it("should display accept-cookies button disabled", () => {
    cy.get("#accept-cookies").should("be.disabled");
  });
});
```