Your first test

A Selenium test has a shape you will write hundreds of times. Here it is, testing Nimbus, the login page you met in the last lecture:

const { Builder, By, until } = require('selenium-webdriver');
const assert = require('assert');

describe('Nimbus login', function () {
  it('shows validation errors for an empty form', async function () {
    const driver = await new Builder().forBrowser('chrome').build();
    await driver.get('/');
    await driver.findElement(By.css('[data-testid="login-button"]')).click();

    const emailError = await driver.wait(
      until.elementLocated(By.css('[data-testid="email-error"]')),
      5000
    );
    assert.ok(await emailError.isDisplayed());
    await driver.quit();
  });
});

Read it as five layers:

1. describe / it come from the test runner (Mocha here). it is one test, and its name is a claim about the app, "shows validation errors for an empty form" tells a reader exactly what broke when it fails.
2. Setup: build() starts the browser, get('/') loads the page.
3. Act like a user: find the Sign in button, click it.
4. Wait, then assert. driver.wait(until.elementLocated(...), 5000) polls until the error message exists (up to 5 seconds), then assert.ok(...) states what must be true. The assert is the test. Without it, the code runs, clicks, finishes, and passes whether the app works or not.
5. Teardown: quit() ends the session. Always.

That fourth point is the difference between code that runs and a test that proves something. A test with no check passes against a completely broken app.

A test file can contain fourteen tests, every one clicking through a form and finishing, with no checks anywhere. The suite is green. It has never tested anything.

When you solve problems here, we check this for real: we break the app on purpose, and your test must turn red.

The official first-script guide: Your first Selenium script.

Now prove it: write this exact test yourself in the problem below, and we will check it catches the bug.