Being good at waiting
Alexander Tarnowski
Using Selenium to test Ajax-intensive pages
Selenium Conference, April 2012
2
3
The DOM and asynchronicity – Challenges
Existing elements may change valuesNew elements may appear Not all Ajax calls have observable side effects
4
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...
5
Home-made wait
timeToWait = 10sloop while timeToWait > 0
if element is found then exit loopsleep decrease timeToWait
end loop
6
Implicit waits
interface Timeouts { Timeouts implicitlyWait(long time, TimeUnit unit); Timeouts setScriptTimeout(long time, TimeUnit unit); Timeouts pageLoadTimeout(long time, TimeUnit unit);}
7
Finders and timeout
findElement() Throws NoSuchElementExceptionRespects implicit waits
findElements()Returns an empty collectionRespects implicit waits
8
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
9
Zero side effect validation
validate(invalid)
“invalid”
validate(valid)
“valid”
SERVER
CLIENT
DOM changes
Nothing
10
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
