Add Chrome DevTools Protocol (CDP) for Performance metrics

[ElSnoMan]

v1.14.0 - 2022.01.27

Overview

Pylenium now uses Selenium v4.1.0! The goal was to start leveraging Selenium 4 features and this release focused on the Performance metrics from the Chrome DevTools Protocol (CDP).

Highlights

Capturing web performance metrics is a powerful feature of web automation. Selenium 4 introduced the ability to leverage CDP which has a Performance API, but it has its limitations. Let's dive into examples because we provide a few ways to capture perf metrics 😄

Chrome DevTools Protocol (CDP)

• selenium.dev docs
• chromedevtools.github.io/devtools-protocol

We created a CDP class so you could call the API directly from Pylenium. Currently, there are only two methods:

# Run any command against the CDP API and get a result. (See the docs linked above for usage examples)
execute_command(cmd: str, cmd_args: Dict) -> Dict

# Return performance metrics like 'ScriptDuration', 'ThreadTime', 'ProcessTime', and 'DomContentLoaded'
get_performance_metrics() -> Dict

Using it is easy!

def test_capture_performance_metrics(py):
    py.visit("https://qap.dev")
    metrics = py.cdp.get_performance_metrics()
    assert metrics["metrics"]
    assert metrics["metrics"][0]["name"] == "Timestamp"
    assert metrics["metrics"][0]["value"] > 0

And in case you're wondering, py.cdp.get_performance_metrics() returns a dictionary that looks kinda like this:

{
  'metrics': [
    {'name': 'Timestamp', 'value': 425608.80694},
    {'name': 'AudioHandlers', 'value': 0},
    {'name': 'ThreadTime', 'value': 0.002074},
    ...
  ]
}

Limitations

⚠️ Selenium says that CDP is meant for Chrome and more experimental for now!

This is good to be aware of. CDP may not work for other browsers or if you're running remotely against something like Selenium Grid.

Pylenium Performance API

The limitations may prevent you from using CDP, but we've got you covered! Pylenium has a Performance API that you can use to capture metrics as well.

💡 Some of these metrics may not be from a "Standard", but they all use W3C objects like PaintTiming. So, you'll see that some of the calculations are made by us, but they have already been applied and used to provide insights and solve problems at a few companies (including Adobe 😎). I hope they can help you too!

Using it is easy as well!

perf = py.performance.get()

This returns a lot of data compared to CDP, so I recommend looking at the performance.py module to see all that's available!

Examples

💡 Calling this method too soon may yield NoneTypes because the browser hasn't generated them yet.

• Store the entire WebPerformance object and print it as a dictionary

  perf = py.performance.get()
  print(perf.dict())

• Get a single data point from WebPerformance

  tti = py.performance.get().time_to_interactive()
  assert tti < 5000 # 5 seconds

What else changed?

• Upgrade to Selenium 4! by @ElSnoMan in upgrade selenium to the newly released version 4! #221
• Fix executable_path deprecation warning for ChromeDriver by @ElSnoMan in Fix executable_path deprecation warning for ChromeDriver #223
• Add EdgeOptions and EdgeService to webdriver_factory by @ElSnoMan in Add EdgeOptions and EdgeService to webdriver_factory #224
• Add new_window() and new_tab() methods to SwitchTo class by @ElSnoMan in Add new_window() and new_tab() methods to SwitchTo class #225

  • This does exactly like what it sounds like 😄

    def test_new_window_and_tab(py: Pylenium):
        # Opens a new, empty browser window and switches to it
        py.switch_to.new_window()
        assert len(py.window_handles) == 2
    
        # Opens a new, empty tab in the current browser window and switches to it
        py.switch_to.new_tab()
        assert len(py.window_handles) == 3

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This discussion was created from the release Add Chrome DevTools Protocol (CDP) for Performance metrics.