What are Cypress fixtures? How do you use test data in Cypress?

cypress/
├── fixtures/
│   ├── users.json          ← test user data
│   ├── products.json       ← product test data
│   ├── login-valid.json    ← valid login creds
│   └── login-invalid.json  ← invalid login creds
├── e2e/
│   └── login.cy.js

// cypress/fixtures/users.json
{
  "validUser": {
    "email": "test@automateqa.com",
    "password": "Test@123",
    "name": "QA Tester"
  },
  "adminUser": {
    "email": "admin@automateqa.com",
    "password": "Admin@123",
    "role": "admin"
  },
  "invalidUser": {
    "email": "wrong@email.com",
    "password": "wrongpass"
  }
}

describe('Login Tests', () => {
  it('should login with valid user', () => {
    cy.fixture('users').then((users) => {
      cy.visit('/login');
      cy.get('#email').type(users.validUser.email);
      cy.get('#password').type(users.validUser.password);
      cy.get('[data-testid="login-btn"]').click();
      cy.get('.user-greeting').should('contain', users.validUser.name);
    });
  });
});

describe('Login Tests', () => {
  beforeEach(function() {
    // Load fixture into this.users — available in all tests
    cy.fixture('users').as('users');
  });

  it('should login with valid credentials', function() {
    const { email, password } = this.users.validUser;
    cy.visit('/login');
    cy.get('#email').type(email);
    cy.get('#password').type(password);
    cy.get('[data-testid="login-btn"]').click();
    cy.url().should('include', '/dashboard');
  });

  it('should reject invalid credentials', function() {
    const { email, password } = this.users.invalidUser;
    cy.visit('/login');
    cy.get('#email').type(email);
    cy.get('#password').type(password);
    cy.get('[data-testid="login-btn"]').click();
    cy.get('.error').should('be.visible');
  });
});

// cypress/fixtures/search-terms.json
// ["Selenium", "Cypress", "Playwright", "TestNG"]

describe('Search Tests', () => {
  it('should search for multiple terms', () => {
    cy.fixture('search-terms').then((terms) => {
      terms.forEach((term) => {
        cy.visit('/');
        cy.get('[data-testid="search"]').clear().type(term);
        cy.get('[data-testid="search-btn"]').click();
        cy.get('[data-testid="result-count"]')
          .should('be.visible')
          .and('not.contain', '0 results');
      });
    });
  });
});

// cypress/fixtures/api-users.json
// [{"id":1,"name":"Alice","role":"QA"},{"id":2,"name":"Bob","role":"Dev"}]

it('should display users from API', () => {
  cy.intercept('GET', '/api/users', { fixture: 'api-users' }).as('getUsers');
  cy.visit('/users');
  cy.wait('@getUsers');
  cy.get('[data-testid="user-row"]').should('have.length', 2);
  cy.contains('Alice').should('be.visible');
});