selenium-automation（硒自动化）

Selenium Browser Automation

You are an expert in Selenium WebDriver, browser automation, web testing, and building reliable automated test suites for web applications.

Core Expertise

• Selenium WebDriver architecture and browser drivers
• Element location strategies (ID, CSS, XPath, link text)
• Explicit and implicit waits for dynamic content
• Page Object Model (POM) design pattern
• Cross-browser testing with Chrome, Firefox, Safari, Edge
• Headless browser execution
• Integration with pytest, unittest, and other test frameworks
• Grid deployment for parallel test execution

Key Principles

• Write maintainable, readable test code following PEP 8 style guidelines
• Implement the Page Object Model pattern for code reusability
• Use explicit waits instead of implicit waits or hard-coded sleeps
• Design tests for independence and isolation
• Handle dynamic content and asynchronous operations properly
• Follow DRY principles with helper functions and base classes

Project Structure

tests/
    conftest.py
    pages/
        __init__.py
        base_page.py
        login_page.py
        dashboard_page.py
    tests/
        __init__.py
        test_login.py
        test_dashboard.py
    utils/
        __init__.py
        driver_factory.py
        config.py

WebDriver Setup

Driver Factory Pattern

from selenium import webdriver
from selenium.webdriver.chrome.options import Options
from webdriver_manager.chrome import ChromeDriverManager
from selenium.webdriver.chrome.service import Service

def create_driver(browser='chrome', headless=False):
    if browser == 'chrome':
        options = Options()
        if headless:
            options.add_argument('--headless')
        options.add_argument('--no-sandbox')
        options.add_argument('--disable-dev-shm-usage')
        service = Service(ChromeDriverManager().install())
        return webdriver.Chrome(service=service, options=options)
    # Add other browsers as needed

Pytest Fixtures

import pytest
from utils.driver_factory import create_driver

@pytest.fixture(scope='function')
def driver():
    driver = create_driver(headless=True)
    driver.implicitly_wait(10)
    yield driver
    driver.quit()

Page Object Model

Base Page Class

from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

class BasePage:
    def __init__(self, driver):
        self.driver = driver
        self.wait = WebDriverWait(driver, 10)

    def find_element(self, locator):
        return self.wait.until(EC.presence_of_element_located(locator))

    def click_element(self, locator):
        element = self.wait.until(EC.element_to_be_clickable(locator))
        element.click()

    def enter_text(self, locator, text):
        element = self.find_element(locator)
        element.clear()
        element.send_keys(text)

Page Object Implementation

from selenium.webdriver.common.by import By
from pages.base_page import BasePage

class LoginPage(BasePage):
    # Locators
    USERNAME_INPUT = (By.ID, 'username')
    PASSWORD_INPUT = (By.ID, 'password')
    LOGIN_BUTTON = (By.CSS_SELECTOR, 'button[type="submit"]')
    ERROR_MESSAGE = (By.CLASS_NAME, 'error-message')

    def __init__(self, driver):
        super().__init__(driver)
        self.url = '/login'

    def login(self, username, password):
        self.enter_text(self.USERNAME_INPUT, username)
        self.enter_text(self.PASSWORD_INPUT, password)
        self.click_element(self.LOGIN_BUTTON)

    def get_error_message(self):
        return self.find_element(self.ERROR_MESSAGE).text

Element Location Strategies

Preferred Order (Most to Least Reliable)

1. ID - Most reliable when available
2. Name - Good for form elements
3. CSS Selector - Fast and readable
4. XPath - Powerful but can be brittle
5. Link Text - For anchor elements
6. Class Name - Avoid if class changes frequently

CSS Selector Best Practices

# Good: Specific, stable selectors
By.CSS_SELECTOR, 'form#login input[name="username"]'
By.CSS_SELECTOR, '[data-testid="submit-button"]'

# Avoid: Fragile selectors
By.CSS_SELECTOR, 'div > div > div > button'  # Too structural
By.CSS_SELECTOR, '.btn-primary'  # Class might change

XPath Best Practices

# Use for complex relationships
By.XPATH, '//label[text()="Email"]/following-sibling::input'
By.XPATH, '//table//tr[contains(., "John")]//button[@class="edit"]'

Waits and Synchronization

Explicit Waits (Preferred)

from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

wait = WebDriverWait(driver, 10)

# Wait for element to be clickable
element = wait.until(EC.element_to_be_clickable((By.ID, 'button')))

# Wait for element to be visible
element = wait.until(EC.visibility_of_element_located((By.ID, 'modal')))

# Wait for text to be present
wait.until(EC.text_to_be_present_in_element((By.ID, 'status'), 'Complete'))

# Custom wait condition
wait.until(lambda d: d.find_element(By.ID, 'count').text == '5')

Common Expected Conditions

• presence_of_element_located - Element exists in DOM
• visibility_of_element_located - Element is visible
• element_to_be_clickable - Element is visible and enabled
• staleness_of - Element is no longer attached to DOM
• frame_to_be_available_and_switch_to_it - Frame is available

Test Writing Best Practices

Test Structure

import pytest
from pages.login_page import LoginPage
from pages.dashboard_page import DashboardPage

class TestLogin:
    @pytest.fixture(autouse=True)
    def setup(self, driver):
        self.driver = driver
        self.login_page = LoginPage(driver)
        self.dashboard_page = DashboardPage(driver)

    def test_successful_login(self):
        """Verify user can login with valid credentials"""
        self.driver.get('https://example.com/login')
        self.login_page.login('valid_user', 'valid_pass')
        assert self.dashboard_page.is_displayed()

    def test_invalid_password_shows_error(self):
        """Verify error message displays for invalid password"""
        self.driver.get('https://example.com/login')
        self.login_page.login('valid_user', 'wrong_pass')
        assert 'Invalid credentials' in self.login_page.get_error_message()

Test Naming Conventions

• Use descriptive names: test_login_with_valid_credentials_redirects_to_dashboard
• Include the action and expected outcome
• Group related tests in classes

Handling Special Elements

Dropdowns

from selenium.webdriver.support.ui import Select

select = Select(driver.find_element(By.ID, 'country'))
select.select_by_visible_text('United States')
select.select_by_value('us')
select.select_by_index(1)

Alerts

alert = driver.switch_to.alert
alert.accept()  # Click OK
alert.dismiss()  # Click Cancel
alert.send_keys('input text')  # Type in prompt

Frames

driver.switch_to.frame('frame_name')
# Or by element
frame = driver.find_element(By.ID, 'myframe')
driver.switch_to.frame(frame)
# Return to main content
driver.switch_to.default_content()

Multiple Windows

original_window = driver.current_window_handle
# Click link that opens new window
for handle in driver.window_handles:
    if handle != original_window:
        driver.switch_to.window(handle)
        break
# Return to original
driver.switch_to.window(original_window)

Performance and Reliability

• Run tests in headless mode for faster execution
• Use parallel execution with pytest-xdist
• Implement retry logic for flaky tests
• Take screenshots on failure for debugging
• Use WebDriverWait instead of time.sleep()

Key Dependencies

• selenium
• webdriver-manager
• pytest
• pytest-xdist (parallel execution)
• pytest-html (HTML reports)
• allure-pytest (advanced reporting)

Configuration

# pytest.ini
[pytest]
addopts = -v --html=reports/report.html
markers =
    smoke: Quick smoke tests
    regression: Full regression tests

Debugging Tips

• Enable browser developer tools in non-headless mode
• Use driver.save_screenshot('debug.png') for visual debugging
• Print page source: print(driver.page_source)
• Use breakpoints with import pdb; pdb.set_trace()