Staff SDET Interview Questions: Synchronization

A: presenceOfElementLocated checks that the element exists in the DOM tree (it can be hidden or invisible). visibilityOfElementLocated checks that the element exists in the DOM AND is displayed with non-zero width and height. elementToBeClickable checks that the element is visible AND enabled (not disabled via attribute). For clicking buttons, elementToBeClickable is required. For reading text, visibilityOfElementLocated is required. For hidden inputs/CSRF tokens, presenceOfElementLocated is used.

A: The W3C WebDriver specification explicitly warns that mixing implicit and explicit waits causes undefined timeout behavior. Explicit wait polls findElement() internally. If implicit wait is active, every failed poll cycle waits the full implicit duration instead of immediately returning to the polling loop. A 10-second explicit wait can end up taking 100+ seconds. Best practice is to set implicit wait to 0 and exclusively use explicit waits.

A: This is classic synchronization flakiness caused by virtualized CI CPU throttling and network latency variance. I resolve it by: (1) Replacing any Thread.sleep() or implicit waits with explicit WebDriverWait and appropriate ExpectedConditions, (2) Waiting for loading overlays/spinners to become invisible before interacting with form fields, (3) Tuning ChromeOptions with --disable-dev-shm-usage and --window-size=1920,1080 to prevent rendering layout shifts, and (4) Centralizing timeouts with configurable CI environment overrides.