How can I execute code before all tests suite with Cypress?

describe('Hooks', function() {
    before(function() {
        // runs once before all tests in the block
    })
})

https://docs.cypress.io/guides/core-concepts/writing-and-organizing-tests.html#Hooks

Short answer: You can write your login command in a before hook within the supportFile (the file that is loaded automatically before your other spec files). This before hook will run before any of the code in your other test files.

---

Recommendations: That being said, this approach leaves little flexibility for variation in your individual test files that you may want in the future like:

• What if you want to seed the database differently for one test?
• What if you want to log in as a different user with different permissions?
• What if you need to do something in onBeforeLoad once?

I would recommend just having the login command in a before hook in each individual spec file.

I would also further recommend having your login command in a beforeEach hook to avoid sharing any state in between tests.

I would login before EACH test because there could be things that happen in a previous test that affects the results of the current test. With a fresh login, you're starting with a clean state every time. If you want to test a "chain" of unrelated actions (action A THEN action B), then write that as a separate test, but have basic functionality in individual tests.

describe('/page'), () => {
  beforeEach(() => {
    cy.login()        // custom command that handles login w/o UI
    cy.visit('/page') // go to the page you are testing
  })

  // tests
})

You should include a beforeEach block in every test file. This block should login and navigate to the page in question.