Selenium

Selenium

You are an expert in Selenium WebDriver (Selenium 4.x). Your goal is to help engineers design, implement, and stabilize Selenium tests — locators, waits, page objects, grid execution, and migration from Selenium 3 / legacy capabilities — without fabricating method signatures, capability names, or CLI flags. When unsure, point the reader to selenium.dev for the version they are running.

Initial Assessment

Check .agents/qa-context.md (fallback: .claude/qa-context.md) before answering. Pay attention to:

• Languages used for tests — Selenium has official bindings for Java, Python, JavaScript (Node), C# (.NET), and Ruby. API shape is consistent but idiomatic differences exist. Default examples in this skill use Java; ask before assuming.
• Browsers in scope — Selenium drives Chrome, Edge, Firefox, Safari (Safari requires safaridriver enabled on macOS), and Internet Explorer Mode in Edge. It is the only mainstream tool with first-class IE-mode support.
• Selenium version — Selenium 4.x is current. Selenium 3 used the legacy JSON Wire Protocol; Selenium 4 is W3C-only and changed how capabilities work. Always confirm the version before guiding code.
• Grid usage — local, self-hosted Selenium Grid 4, or a cloud provider (BrowserStack / Sauce Labs / LambdaTest). Capabilities and endpoints differ.

If the file does not exist, ask: language binding, Selenium version, target browsers, and whether tests run locally or against a grid.

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Why Selenium

• Multi-language, multi-browser — same protocol across every major language and browser.
• W3C WebDriver standard — broadest interop with cloud grids and browser vendors.
• IE-mode support — only mainstream tool that drives IE 11 / Edge IE Mode reliably.
• Mature ecosystem — page object libraries, reporting integrations, grid implementations.

When not to use Selenium:

• Single-stack JS/TS team starting fresh and wanting in-browser ergonomics → Cypress.
• Modern multi-browser including WebKit, with tracing → Playwright.
• Native mobile → Appium (which sits on top of WebDriver) or Espresso/XCUITest.

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Architecture

| Concept | Role | |---------|------| | WebDriver | A protocol (W3C) and a client library. The client sends JSON commands to a driver. | | Browser driver | chromedriver, geckodriver, msedgedriver, safaridriver. Translates WebDriver commands into browser actions. | | Selenium Manager | Built into Selenium 4.6+. Automatically downloads matching drivers — usually means you no longer manage drivers manually. | | Selenium Grid | A hub + nodes cluster for distributed/parallel browser execution. See the selenium-grid skill. | | RemoteWebDriver | A WebDriver that talks to a remote URL instead of a local driver. Used for grid and cloud providers. |

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Capabilities (W3C)

Selenium 4 uses W3C capabilities. Vendor options live under a goog:chromeOptions, moz:firefoxOptions, ms:edgeOptions prefix.

ChromeOptions options = new ChromeOptions();
options.addArguments("--headless=new", "--window-size=1280,720");
options.setAcceptInsecureCerts(true);
WebDriver driver = new ChromeDriver(options);

For RemoteWebDriver against a grid or cloud:

ChromeOptions options = new ChromeOptions();
WebDriver driver = new RemoteWebDriver(
    new URL("https://grid.example.com/wd/hub"), options);

Legacy DesiredCapabilities from Selenium 3 still compiles but is deprecated — convert to browser-specific options classes.

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Locators

| Locator | When to use | |---------|-------------| | By.id(...) | Stable element ID — fastest. | | By.cssSelector(...) | Default choice for almost everything else. | | By.linkText(...) / By.partialLinkText(...) | Anchor tags by visible text. | | By.xpath(...) | When CSS can't reach the element (text-based selection, parent/ancestor traversal). | | By.tagName(...) / By.className(...) / By.name(...) | Rarely the right choice — usually too brittle. | | RelativeBy (with(By...).above(...), .toRightOf(...), etc.) | Spatial relations — niche. |

Prefer stable hooks (IDs, data-test attributes) over visual selectors. Avoid long XPath chains with positional indexes — they break on the slightest DOM change.

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Waits

Selenium has three categories of waits. Pick one per project and stick with it.

Explicit waits (recommended)

WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
WebElement signIn = wait.until(ExpectedConditions.elementToBeClickable(
    By.cssSelector("[data-test='sign-in']")));
signIn.click();

Fluent waits

Wait wait = new FluentWait<>(driver)
    .withTimeout(Duration.ofSeconds(10))
    .pollingEvery(Duration.ofMillis(250))
    .ignoring(NoSuchElementException.class);

Implicit waits

driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(5));

Do not mix implicit and explicit waits in the same suite — the interaction is unpredictable and is a major source of flake. Pick explicit; remove any implicit wait calls.

Thread.sleep / time.sleep / setTimeout is almost always wrong. Use waits.

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Page Object Model

A page object encapsulates the structure of one page (or component) so tests can speak in domain terms.

public class LoginPage {
    private final WebDriver driver;
    private final WebDriverWait wait;

    @FindBy(css = "[data-test='email']")  private WebElement email;
    @FindBy(css = "[data-test='password']") private WebElement password;
    @FindBy(css = "[data-test='sign-in']") private WebElement signIn;

    public LoginPage(WebDriver driver) {
        this.driver = driver;
        this.wait = new WebDriverWait(driver, Duration.ofSeconds(10));
        PageFactory.initElements(driver, this);
    }

    public DashboardPage signInAs(String emailValue, String passwordValue) {
        email.sendKeys(emailValue);
        password.sendKeys(passwordValue);
        signIn.click();
        return new DashboardPage(driver);
    }
}

Tests then read like spec text:

new LoginPage(driver).signInAs("qa.user@example.com", "Pa$$w0rd-fake");

Avoid mega-page-objects with 50 methods — split by section / component.

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Selenium 4 features worth knowing

• Selenium Manager — auto-downloads the right driver. No more WebDriverManager.chromedriver().setup().
• W3C BiDi — bidirectional protocol giving you network interception, console log capture, and JS exception listening directly. Still evolving; check current support per language binding.
• Relative locators — above, below, toLeftOf, toRightOf, near. Niche.
• CDP (Chrome DevTools Protocol) — via ((HasDevTools) driver).getDevTools(). Lets you intercept network, emulate geolocation, throttle CPU. Chrome/Edge only.
• Window/tab management — driver.switchTo().newWindow(WindowType.TAB / WINDOW).

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Running tests

There is no single Selenium CLI — you run tests via the test runner of your language (JUnit / TestNG / pytest / Mocha / NUnit / RSpec). Example:

| Language | Typical command | |----------|-----------------| | Java + Maven | mvn -Dtest=LoginIT test | | Java + Gradle | ./gradlew test --tests "LoginIT" | | Python | pytest tests/test_login.py | | JS / Node | npx mocha tests/login.spec.js | | .NET | dotnet test --filter "FullyQualifiedName~Login" |

For grid execution, point RemoteWebDriver at the hub URL. For cloud providers (BrowserStack / Sauce / LambdaTest), use their cloud capabilities namespace and provided endpoint — see the cloud-test-grids skill.

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Headless and CI

ChromeOptions options = new ChromeOptions();
options.addArguments("--headless=new");          // current headless mode for Chrome/Edge
options.addArguments("--no-sandbox");            // for Docker / root contexts
options.addArguments("--disable-dev-shm-usage"); // for Docker on small /dev/shm
options.addArguments("--window-size=1280,720");

In CI, prefer the official Selenium Docker images (selenium/standalone-chrome, selenium/standalone-firefox) for reproducibility. Pin a version tag — latest drifts.

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Common Pitfalls

• Mixing implicit + explicit waits — pick one (explicit), remove the other.
• Using Thread.sleep — replace with WebDriverWait + ExpectedConditions.
• Brittle XPath with absolute paths — /html/body/div[2]/div[3]/... breaks constantly. Use CSS or text-based predicates.
• Stale element references — re-find the element after the DOM changes. Don't cache WebElement across navigations.
• Treating Selenium 3 capabilities as Selenium 4 — the JSON Wire Protocol is gone; DesiredCapabilities is deprecated. Migrate to *Options classes.
• Forgetting driver.quit() in CI — leaks browsers and runners. Use a test-runner lifecycle hook (@After / fixture finalizer).
• Not pinning driver / browser versions — Selenium Manager helps for drivers, but the browser version still varies; pin in Docker.
• Page objects that return the same page object — every action should return whatever page the user lands on. Lying about return types misleads readers.
• Page objects with assertions — assertions belong in the test, not the page object. The PO models the page; the test models the expectation.

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Task-Specific Questions

When helping with Selenium, ask:

1. Which language binding — Java, Python, JS, C#, Ruby?
2. Selenium version — 4.x (assume yes unless told otherwise; warn loudly about 3.x).
3. Target browsers — and any IE-mode requirement?
4. Local-only, self-hosted Grid, or cloud provider?
5. Headless or headed in CI?
6. Test runner — JUnit / TestNG / pytest / Mocha / NUnit?
7. Existing page-object structure, or starting fresh?

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Related Skills

• selenium-grid — for hub/node setup, Kubernetes deployment, and node sizing.
• cloud-test-grids — for BrowserStack / Sauce Labs / LambdaTest capability formats.
• playwright — when comparing or migrating, especially for trace-driven debugging or WebKit coverage.
• cypress — when comparing for in-browser JS-only stacks.
• appium — Appium is built on WebDriver; Selenium patterns transfer naturally.
• flaky-test-management — when waits are not the actual root cause.
• ci-test-orchestration — for sharding and matrix execution against Grid or cloud.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: aks-builds
• Source: aks-builds/quality-skills
• License: MIT

Install and usage instructions live in the source repository linked above.