Element waiting mechanism

Background introduction

In many test scenarios , We need to keep the running speed of the script consistent with the response speed of the program . therefore ,WebDriver It provides two mechanisms: implicit waiting and display waiting .

An implicit wait

For solving problems caused by Network delay Or use Ajax Dynamically load elements Resulting in inconsistent program response times , It's very effective .
After setting the implicit wait time ,WebDriver It will continuously detect and search within a certain period of time DOM, To find one or more elements that are not immediately loaded successfully and available .
In general , The default timeout for implicit waiting is set to 0.

self.driver.implicitly_wait(30)

Timeout element not found , It will be thrown out. NoSuchElementException It's abnormal .

According to wait

Display waiting is more controllable than implicit waiting .
Show that waiting can only work on test cases with only synchronous requirements .
WebDriver Provides WebDriverWait Classes and expected_conditions Class to implement display wait .
There are two uses ：

WebDriverWait(self.driver, 10).until(lambda s:s.find_element_by_id("select-language").get_attribute("length")=="3")

account = WebDriverWait(self.driver, 10) \
　　　　　　.until(expected_conditions. \
　　　　　　　visibility_of_element_located \
　　　　　　　　　((By.LINK_TEXT, "ACCOUNT")))
　　　　account.click()

If the timeout , The element is still not visible , It will be thrown out. TimeoutException abnormal .

expected_conditions class

Common waiting conditions are as follows ：

Determine whether an element exists

have access to element_to _be_clickable Wait and check if an element is available . When the target element is clickable or available , This method returns the located target element to the test script .
It can also be used as a judgment condition by detecting whether the specified document appears in the title , For example, we can use title_contains Expected condition detection .

Judge whether it exists Alerts

Display wait can also be applied to warnings and page frames .Alert_is_present The expected decision condition can be used to detect whether the warning window appears , And return the warning window to the script , For subsequent actions .

alert = WebDriverWait(self.driver, 10).until(expected_conditions.alert_is_present())