Error messages¶

When an assertion fails, selenium-expect raises an AssertionError with a descriptive multi-line message.

Structure¶

Expected {entity} {condition}, but got {actual}
  Expected: {expected}
  Actual:   {actual}
  Element:  {truncated_html}
  Waited:   {elapsed_ms}ms ({poll_count} polls at {polling_interval}s interval)
  Message:  {custom_message}
  Timeline: [poll N: actual, ...]

Example¶

Expected <h1> to have text 'Hello, World!', but got Goodbye
  Expected: Hello, World!
  Actual:   Goodbye
  Element:  <h1 id="greeting">Goodbye</h1>
  Waited:   5001ms (10 polls at 0.5s interval)
  Timeline: [poll 6: Goodbye, poll 7: Goodbye, poll 8: Goodbye, poll 9: Goodbye, poll 10: Goodbye]

Fields¶

Field	Description
`entity`	Description of the target (e.g. `<h1 id="greeting">`, `driver`, `ShadowRoot`)
`condition`	What was expected (e.g. `to have text 'Hello'`)
`expected`	Expected value
`actual`	Actual value at the last poll
`Element`	Truncated `outerHTML` of the element (first 200 chars)
`Waited`	Total time waited, poll count, and interval
`Message`	Custom message passed via `expect(target, message="...")`
`Timeline`	Last 5 poll results for debugging intermittent issues

Custom messages¶

Pass a message to expect() for additional context:

expect(element, message="Login button should be visible after auth").to_be_visible()

Debug mode¶

Enable debug logging to see retry loop details in real time:

from selenium_expect import set_debug_mode

set_debug_mode(True)

This prints poll count, elapsed time, and actual values to the selenium_expect logger.

Screenshots¶

Enable automatic screenshot capture on failure:

from selenium_expect import set_screenshot_on_failure

set_screenshot_on_failure(True, path="./screenshots/")

Screenshots are saved as screenshot_{timestamp}_{condition}.png.

Sensitive data in error output

Failure messages include the element's outerHTML and actual values (texts, attribute values, cookie values, JS results). These may contain tokens or personal data — keep test logs private, and avoid asserting on secrets with descriptive messages if logs are shared.

Examples¶

Understanding the timeline¶

The timeline shows the last 5 poll results, which helps diagnose intermittent issues:

Expected <span id="status"> to have text 'Ready', but got Loading
  Expected: Ready
  Actual:   Loading
  Element:  <span id="status">Loading</span>
  Waited:   5001ms (10 polls at 0.5s interval)
  Timeline: [poll 6: Loading, poll 7: Loading, poll 8: Loading, poll 9: Loading, poll 10: Loading]

If the value was changing during the wait, the timeline would show it:

Expected <span id="status"> to have text 'Ready', but got Loading
  Expected: Ready
  Actual:   Loading
  Element:  <span id="status">Loading</span>
  Waited:   5001ms (10 polls at 0.5s interval)
  Timeline: [poll 6: Pending, poll 7: Loading, poll 8: Loading, poll 9: Loading, poll 10: Loading]

Using custom messages for context¶

# Add context to error messages
expect(
    driver.find_element(By.ID, "checkout-btn"),
    message="Checkout button should be enabled after cart has items"
).to_be_enabled()

expect(
    driver,
    message="Should redirect to dashboard after login"
).to_have_url_contains("/dashboard")

Debug mode output¶

When debug mode is enabled, each poll logs details on the selenium_expect logger (DEBUG level):

poll 1: passed=False actual=False — 0.4ms elapsed
poll 2: passed=False actual=False — 500.9ms elapsed
poll 3: passed=True actual=True — 1001.8ms elapsed

Screenshots on failure¶

from selenium_expect import set_screenshot_on_failure

# Enable with a custom path
set_screenshot_on_failure(True, path="./screenshots/")

# Now any assertion failure saves a screenshot
expect(element).to_be_visible(timeout=5)
# If this fails, you'll find: ./screenshots/screenshot_20240101_120000_to_be_visible.png