Performance metrics via DevTools in Selenium Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are performance metrics in web testing?

Performance metrics are measurements that show how fast and efficiently a web page or application loads and runs. They help identify slow parts and improve user experience.

beginner

How does Chrome DevTools help in performance testing?

Chrome DevTools provides tools to record and analyze page load times, CPU usage, memory, and network activity. It helps testers find bottlenecks and optimize performance.

intermediate

What is the role of Selenium with DevTools Protocol in performance testing?

Selenium can connect to Chrome DevTools Protocol to capture performance data during automated tests. This allows testers to measure metrics like page load time programmatically.

beginner

Name two key performance metrics you can get from DevTools.

Two key metrics are: 1) Time to First Byte (TTFB) - how fast the server responds, and 2) DOMContentLoaded - when the page structure is ready.

intermediate

Why is it important to automate performance metric collection?

Automating performance metric collection saves time, ensures consistency, and helps catch performance issues early during development or regression testing.

Which tool allows you to capture performance metrics during Selenium tests?

A JUnit

B Chrome DevTools Protocol

C Postman

D Git

Chrome DevTools Protocol integrates with Selenium to capture performance data during tests.

What does the metric 'Time to First Byte' measure?

A Time to execute JavaScript

B Time to load all images

C Time to render CSS

D Time until the first byte is received from the server

TTFB measures how quickly the server responds with the first byte of data.

Which Selenium feature is used to access DevTools performance metrics?

A WebDriverWait

B Actions class

C ChromeDriver with DevTools Protocol

D PageFactory

ChromeDriver supports DevTools Protocol to access performance metrics.

Why should performance metrics be collected during automated tests?

A To detect performance issues early and consistently

B To increase test execution time

C To avoid writing test scripts

D To reduce browser compatibility

Collecting metrics during tests helps find performance problems early and reliably.

Which of these is NOT a typical performance metric from DevTools?

A Number of test cases

B Memory consumption

C CPU usage

D Network activity

Number of test cases is unrelated to performance metrics.

Explain how Selenium integrates with Chrome DevTools Protocol to collect performance metrics.

Think about how Selenium controls the browser and talks to DevTools.

List and describe three important performance metrics you can monitor using DevTools.

Focus on metrics that show how fast the page loads and becomes interactive.

Practice

1. What is the main purpose of using DevTools performance metrics in Selenium Java tests?

easy

A. To handle browser alerts automatically

B. To locate elements on the web page

C. To take screenshots during test execution

D. To measure page load speed and browser performance

Solution

1. Step 1: Understand DevTools role in Selenium

   DevTools integration allows Selenium to collect browser performance data like load times.

2. Step 2: Identify the purpose of performance metrics

   Performance metrics help measure page speed and resource usage to improve user experience.

3. Final Answer:

   To measure page load speed and browser performance -> Option D

4. Quick Check:

   Performance metrics = page speed measurement [OK]

Hint: Performance metrics measure speed, not element location [OK]

Common Mistakes:

• Confusing performance metrics with element locators
• Thinking DevTools handles alerts
• Assuming screenshots are related to performance

2. Which Java code snippet correctly enables performance monitoring using DevTools in Selenium?

easy

A. devTools.send(Performance.enable());

B. driver.get("https://example.com");

C. driver.manage().timeouts().pageLoadTimeout(Duration.ofSeconds(10));

D. devTools.send(Network.enable(Optional.empty(), Optional.empty(), Optional.empty()));

Solution

1. Step 1: Identify the correct DevTools command for performance

   The Performance domain in DevTools is enabled by calling Performance.enable().

2. Step 2: Check other options for correctness

   devTools.send(Network.enable(Optional.empty(), Optional.empty(), Optional.empty())); enables Network, not Performance. driver.manage().timeouts().pageLoadTimeout(Duration.ofSeconds(10)); sets timeout, and B loads a page.

3. Final Answer:

   devTools.send(Performance.enable()); -> Option A

4. Quick Check:

   Enable performance with Performance.enable() [OK]

Hint: Use Performance.enable() to start performance monitoring [OK]

Common Mistakes:

• Using Network.enable() instead of Performance.enable()
• Confusing timeout settings with performance enabling
• Calling driver.get() instead of enabling metrics

3. Given the following code snippet, what will be the output type of metrics.getMetrics()?

DevTools devTools = driver.getDevTools();
devTools.createSession();
devTools.send(Performance.enable());
PerformanceMetrics metrics = devTools.send(Performance.getMetrics());
System.out.println(metrics.getMetrics().get(0).getName());

medium

A. A boolean indicating if metrics are enabled

B. An integer value of the first metric

C. A String representing the name of the first performance metric

D. A list of WebElement objects

Solution

1. Step 1: Understand Performance.getMetrics() return type

   It returns a PerformanceMetrics object containing a list of Metric objects, each with a name and value.

2. Step 2: Analyze metrics.getMetrics().get(0).getName()

   This accesses the first Metric's name, which is a String describing the metric.

3. Final Answer:

   A String representing the name of the first performance metric -> Option C

4. Quick Check:

   getName() returns String metric name [OK]

Hint: getName() returns metric name as String, not value [OK]

Common Mistakes:

• Assuming getName() returns a number
• Confusing metrics with WebElements
• Expecting a boolean from getMetrics()

4. Identify the error in this Selenium Java code snippet that tries to enable performance metrics:

DevTools devTools = driver.getDevTools();
devTools.send(Performance.enable());
devTools.createSession();

medium

A. Performance.enable() requires parameters

B. createSession() must be called before sending commands

C. DevTools cannot be used with ChromeDriver

D. No error, code is correct

Solution

1. Step 1: Check the order of DevTools commands

   Session must be created before sending any DevTools commands like Performance.enable().

2. Step 2: Verify method usage

   Calling Performance.enable() before createSession() causes an error because no session exists yet.

3. Final Answer:

   createSession() must be called before sending commands -> Option B

4. Quick Check:

   Call createSession() first, then enable performance [OK]

Hint: Always createSession() before sending DevTools commands [OK]

Common Mistakes:

• Calling enable() before createSession()
• Thinking Performance.enable() needs parameters
• Assuming DevTools is unsupported in ChromeDriver

5. You want to measure the page load time using Selenium Java and DevTools. Which approach correctly captures the 'DomContentLoaded' metric after page load?

hard

A. Enable performance, load page, then get metrics and filter for 'DomContentLoaded'

B. Load page first, then enable performance and get metrics immediately

C. Enable performance, get metrics before loading page, then load page

D. Only use driver.manage().timeouts().pageLoadTimeout() to measure load time

Solution

1. Step 1: Enable performance monitoring before page load

   Performance must be enabled before loading the page to capture all metrics during load.

2. Step 2: Load the page and then retrieve metrics filtering for 'DomContentLoaded'

   After page load, get metrics and select the 'DomContentLoaded' metric to measure load time.

3. Final Answer:

   Enable performance, load page, then get metrics and filter for 'DomContentLoaded' -> Option A

4. Quick Check:

   Enable first, load page, then get metrics [OK]

Hint: Enable before load, get metrics after load for accurate timing [OK]

Common Mistakes:

• Enabling performance after page load misses metrics
• Getting metrics before loading page
• Relying only on timeout settings for load time