🧪 Add e2e tests with Cypress

frontend/cypress/integration-examples/1-getting-started/todo.spec.js

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+/// <reference types="cypress" />
+
+// Welcome to Cypress!
+//
+// This spec file contains a variety of sample tests
+// for a todo list app that are designed to demonstrate
+// the power of writing tests in Cypress.
+//
+// To learn more about how Cypress works and
+// what makes it such an awesome testing tool,
+// please read our getting started guide:
+// https://on.cypress.io/introduction-to-cypress
+
+describe('example to-do app', () => {
+  beforeEach(() => {
+    // Cypress starts out with a blank slate for each test
+    // so we must tell it to visit our website with the `cy.visit()` command.
+    // Since we want to visit the same URL at the start of all our tests,
+    // we include it in our beforeEach function so that it runs before each test
+    cy.visit('https://example.cypress.io/todo')
+  })
+
+  it('displays two todo items by default', () => {
+    // We use the `cy.get()` command to get all elements that match the selector.
+    // Then, we use `should` to assert that there are two matched items,
+    // which are the two default items.
+    cy.get('.todo-list li').should('have.length', 2)
+
+    // We can go even further and check that the default todos each contain
+    // the correct text. We use the `first` and `last` functions
+    // to get just the first and last matched elements individually,
+    // and then perform an assertion with `should`.
+    cy.get('.todo-list li').first().should('have.text', 'Pay electric bill')
+    cy.get('.todo-list li').last().should('have.text', 'Walk the dog')
+  })
+
+  it('can add new todo items', () => {
+    // We'll store our item text in a variable so we can reuse it
+    const newItem = 'Feed the cat'
+
+    // Let's get the input element and use the `type` command to
+    // input our new list item. After typing the content of our item,
+    // we need to type the enter key as well in order to submit the input.
+    // This input has a data-test attribute so we'll use that to select the
+    // element in accordance with best practices:
+    // https://on.cypress.io/selecting-elements
+    cy.get('[data-test=new-todo]').type(`${newItem}{enter}`)
+
+    // Now that we've typed our new item, let's check that it actually was added to the list.
+    // Since it's the newest item, it should exist as the last element in the list.
+    // In addition, with the two default items, we should have a total of 3 elements in the list.
+    // Since assertions yield the element that was asserted on,
+    // we can chain both of these assertions together into a single statement.
+    cy.get('.todo-list li')
+      .should('have.length', 3)
+      .last()
+      .should('have.text', newItem)
+  })
+
+  it('can check off an item as completed', () => {
+    // In addition to using the `get` command to get an element by selector,
+    // we can also use the `contains` command to get an element by its contents.
+    // However, this will yield the <label>, which is lowest-level element that contains the text.
+    // In order to check the item, we'll find the <input> element for this <label>
+    // by traversing up the dom to the parent element. From there, we can `find`
+    // the child checkbox <input> element and use the `check` command to check it.
+    cy.contains('Pay electric bill')
+      .parent()
+      .find('input[type=checkbox]')
+      .check()
+
+    // Now that we've checked the button, we can go ahead and make sure
+    // that the list element is now marked as completed.
+    // Again we'll use `contains` to find the <label> element and then use the `parents` command
+    // to traverse multiple levels up the dom until we find the corresponding <li> element.
+    // Once we get that element, we can assert that it has the completed class.
+    cy.contains('Pay electric bill')
+      .parents('li')
+      .should('have.class', 'completed')
+  })
+
+  context('with a checked task', () => {
+    beforeEach(() => {
+      // We'll take the command we used above to check off an element
+      // Since we want to perform multiple tests that start with checking
+      // one element, we put it in the beforeEach hook
+      // so that it runs at the start of every test.
+      cy.contains('Pay electric bill')
+        .parent()
+        .find('input[type=checkbox]')
+        .check()
+    })
+
+    it('can filter for uncompleted tasks', () => {
+      // We'll click on the "active" button in order to
+      // display only incomplete items
+      cy.contains('Active').click()
+
+      // After filtering, we can assert that there is only the one
+      // incomplete item in the list.
+      cy.get('.todo-list li')
+        .should('have.length', 1)
+        .first()
+        .should('have.text', 'Walk the dog')
+
+      // For good measure, let's also assert that the task we checked off
+      // does not exist on the page.
+      cy.contains('Pay electric bill').should('not.exist')
+    })
+
+    it('can filter for completed tasks', () => {
+      // We can perform similar steps as the test above to ensure
+      // that only completed tasks are shown
+      cy.contains('Completed').click()
+
+      cy.get('.todo-list li')
+        .should('have.length', 1)
+        .first()
+        .should('have.text', 'Pay electric bill')
+
+      cy.contains('Walk the dog').should('not.exist')
+    })
+
+    it('can delete all completed tasks', () => {
+      // First, let's click the "Clear completed" button
+      // `contains` is actually serving two purposes here.
+      // First, it's ensuring that the button exists within the dom.
+      // This button only appears when at least one task is checked
+      // so this command is implicitly verifying that it does exist.
+      // Second, it selects the button so we can click it.
+      cy.contains('Clear completed').click()
+
+      // Then we can make sure that there is only one element
+      // in the list and our element does not exist
+      cy.get('.todo-list li')
+        .should('have.length', 1)
+        .should('not.have.text', 'Pay electric bill')
+
+      // Finally, make sure that the clear button no longer exists.
+      cy.contains('Clear completed').should('not.exist')
+    })
+  })
+})