Test With A Different Item Every Day

Recently a user asked in Filip Hric's Discord server how to pick a different test item daily to use in their Cypress tests.

An excellent question. Sometimes we have a lot of test items, but we want to pick a random one daily. Here is my solution:

• take the current timestamp and convert to the number of days since the start of JS epoch (1970)
• take the module of days vs test items, this gives you a test item's index. The index changes daily and "wraps" around to the first item when all items have been tested.

A sample code to pick an item:

const now = new Date()
// divide the timestamp by the number of milliseconds in 1 full day
const fullDaysSinceEpoch = Math.floor(now / 8.64e7)
const testIndex = fullDaysSinceEpoch % list.length
const testItem = list[testIndex]

🎁 You can find the full source code in the repo bahmutov/cypress-test-every-day.

Let's say the application is showing a randomized list of fruits. We know we want to eventually test every fruit from the JSON file test-fruits.json

test-fruits.json

["Apples 655", "Grapes 1001", "Pears 499"]

Our spec file and test JSON file are placed in the repo folder:

app/
  test-fruits.json
  cypress.config.js

  public/
    index.html
    app.js
  cypress/
    e2e/
      spec.cy.js

Let's pick a random test fruit from the JSON file. We can read the file using cy.readFile command

cypress/e2e/spec.cy.js

it('shows one of the fruits', () => {
  cy.visit('public/index.html')
  cy.readFile('test-fruits.json')
    .its('length')
    .then((n) => {
      cy.get('#fruit li').should('have.length', n)
    })

  cy.readFile('test-fruits.json').then((list) => {
    const now = new Date()
    const fullDaysSinceEpoch = Math.floor(now / 8.64e7)
    const testFruitIndex = fullDaysSinceEpoch % list.length
    const testFruit = list[testFruitIndex]
    cy.log(
      `picked test fruit ${fullDaysSinceEpoch} ${testFruitIndex}: ${testFruit}`,
    )
    cy.contains('#fruit li', testFruit)
  })
})

Tip: want to pick a new test item hourly? Divide the timestamp by the number of milliseconds in one hour.

Tip 2: want to pick consistent item locally and on the CI server? Use UTC timestamp.

Of course, if our test data comes from a JSON file, we can simply import it into our spec

cypress/e2e/spec2.cy.js

import testFruits from '../../test-fruits.json'

it('shows one of the fruits', () => {
  cy.visit('public/index.html')
  cy.get('#fruit li').should('have.length', testFruits.length)

  const now = new Date()
  const fullDaysSinceEpoch = Math.floor(now / 8.64e7)
  const testFruitIndex = fullDaysSinceEpoch % testFruits.length
  const testFruit = testFruits[testFruitIndex]
  cy.log(
    `picked test fruit ${fullDaysSinceEpoch} ${testFruitIndex}: ${testFruit}`,
  )
  cy.contains('#fruit li', testFruit)
})

Works the same way

For more on JSON fixtures, read my blog post Import Cypress fixtures.