Your automation suite has 500 tests and takes 2 hours to run. How do you reduce execution time?

<!-- testng.xml — run methods in parallel with 10 threads -->
<suite name="Suite" parallel="methods" thread-count="10">
    <test name="Regression">
        <classes>
            <class name="tests.LoginTest"/>
            <class name="tests.CartTest"/>
            <class name="tests.CheckoutTest"/>
        </classes>
    </test>
</suite>

// Run 50 tests simultaneously on Selenium Grid
WebDriver driver = new RemoteWebDriver(
    new URL("http://selenium-hub:4444/wd/hub"),
    new ChromeOptions()
);

<!-- 50 simultaneous threads across Grid nodes -->
<suite parallel="methods" thread-count="50">

# Pipeline Stage 1: Smoke (15 tests, 3 min) — every commit
mvn test -Dgroups="smoke" -Dthread-count=5

# Pipeline Stage 2: Regression (500 tests, 20 min) — every PR
mvn test -Dgroups="regression" -Dthread-count=20

# Pipeline Stage 3: Full suite (nightly only)
mvn test -Dthread-count=50

// SLOW: Login via UI every test (30 seconds each)
// × 500 tests = 4 hours just on login!
@BeforeMethod
public void loginViaUI() {
    driver.get(baseUrl + "/login");
    driver.findElement(By.id("username")).sendKeys("admin");
    driver.findElement(By.id("password")).sendKeys("pass");
    driver.findElement(By.id("loginBtn")).click();
}

// FAST: Login via API once, inject cookie
@BeforeSuite
public void loginViaAPI() {
    Response r = RestAssured.given()
        .body("{\"email\":\"admin@test.com\",\"password\":\"pass\"}")
        .post("/api/login");
    this.authCookie = r.getCookie("session");
}

@BeforeMethod
public void injectSession() {
    driver.get(baseUrl);
    driver.manage().addCookie(new Cookie("session", authCookie));
    // 2 seconds instead of 30!
}

// SLOW: Fixed waits everywhere
Thread.sleep(5000); // wasting time 500× = 41 minutes wasted!

// FAST: Wait only as long as needed
wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("result")));
// Continues as soon as element appears

// Headless is 20-40% faster than headed
options.addArguments("--headless=new");

Before:  2 hours sequential
After:
  Step 1 (parallel, 10 threads): 12 minutes
  Step 2 (Grid, 50 threads):      3 minutes
  Step 3 (API login):              -40 min saved
  Step 4 (no Thread.sleep):        -30 min saved
Final: ~8-12 minutes for 500 tests on Grid