being good at waiting - using selenium to test ajax-intensive pages
TRANSCRIPT
Being good at waiting
Alexander Tarnowski
Using Selenium to test Ajax-intensive pages
Selenium Conference, April 2012
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The DOM and asynchronicity – Challenges
Existing elements may change valuesNew elements may appear Not all Ajax calls have observable side effects
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The naive approach doesn’t work
It’s uglyDifferent loads on the target host make setting the correct interval difficult Time lost! Imagine 1000+ tests where each test spends 2 seconds sleeping...
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Home-made wait
timeToWait = 10sloop while timeToWait > 0
if element is found then exit loopsleep decrease timeToWait
end loop
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Implicit waits
interface Timeouts { Timeouts implicitlyWait(long time, TimeUnit unit); Timeouts setScriptTimeout(long time, TimeUnit unit); Timeouts pageLoadTimeout(long time, TimeUnit unit);}
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Finders and timeout
findElement() Throws NoSuchElementExceptionRespects implicit waits
findElements()Returns an empty collectionRespects implicit waits
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WebDriverWait
new WebDriverWait(webDriver, 5).until(new ExpectedCondition<WebElement>() { public WebElement apply(WebDriver webDriver) { return webDriver.findElement(By.id("some id")); }});
Parameters: timeout, polling interval, ignored exceptions, error messageIgnores exceptions by default
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Zero side effect validation
validate(invalid)
“invalid”
validate(valid)
“valid”
SERVER
CLIENT
DOM changes
Nothing
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How to wait – Conclusion
Method When
Sleep Never
Home-made sleep Once – and remove it
Implicit waits When you really, really don’t care about Ajax
WebDriverWait Whenever you can
Poll an ”Ajax status” variable When there are no observable side effects