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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 01:47:29 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 01:47:29 +0000 |
| commit | 0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d (patch) | |
| tree | a31f07c9bcca9d56ce61e9a1ffd30ef350d513aa /testing/marionette/client/docs/advanced/stale.rst | |
| parent | Initial commit. (diff) | |
| download | firefox-esr-0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d.tar.xz firefox-esr-0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d.zip | |
Adding upstream version 115.8.0esr.upstream/115.8.0esr
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'testing/marionette/client/docs/advanced/stale.rst')
| -rw-r--r-- | testing/marionette/client/docs/advanced/stale.rst | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/testing/marionette/client/docs/advanced/stale.rst b/testing/marionette/client/docs/advanced/stale.rst new file mode 100644 index 0000000000..885083993c --- /dev/null +++ b/testing/marionette/client/docs/advanced/stale.rst @@ -0,0 +1,76 @@ +Dealing with Stale Elements +=========================== +.. py:currentmodule:: marionette_driver.marionette + +Marionette does not keep a live representation of the DOM saved. All it can do +is send commands to the Marionette server which queries the DOM on the client's +behalf. References to elements are also not passed from server to client. A +unique id is generated for each element that gets referenced and a mapping of +id to element object is stored on the server. When commands such as +:func:`~HTMLElement.click` are run, the client sends the element's id along +with the command. The server looks up the proper DOM element in its reference +table and executes the command on it. + +In practice this means that the DOM can change state and Marionette will never +know until it sends another query. For example, look at the following HTML:: + + <head> + <script type=text/javascript> + function addDiv() { + var div = document.createElement("div"); + document.getElementById("container").appendChild(div); + } + </script> + </head> + + <body> + <div id="container"> + </div> + <input id="button" type=button onclick="addDiv();"> + </body> + +Care needs to be taken as the DOM is being modified after the page has loaded. +The following code has a race condition:: + + button = client.find_element('id', 'button') + button.click() + assert len(client.find_elements('css selector', '#container div')) > 0 + + +Explicit Waiting and Expected Conditions +---------------------------------------- +.. py:currentmodule:: marionette_driver + +To avoid the above scenario, manual synchronisation is needed. Waits are used +to pause program execution until a given condition is true. This is a useful +technique to employ when documents load new content or change after +``Document.readyState``'s value changes to "complete". + +The :class:`Wait` helper class provided by Marionette avoids some of the +caveats of ``time.sleep(n)``. It will return immediately once the provided +condition evaluates to true. + +To avoid the race condition in the above example, one could do:: + + from marionette_driver import Wait + + button = client.find_element('id', 'button') + button.click() + + def find_divs(): + return client.find_elements('css selector', '#container div') + + divs = Wait(client).until(find_divs) + assert len(divs) > 0 + +This avoids the race condition. Because finding elements is a common condition +to wait for, it is built in to Marionette. Instead of the above, you could +write:: + + from marionette_driver import Wait + + button = client.find_element('id', 'button') + button.click() + assert len(Wait(client).until(expected.elements_present('css selector', '#container div'))) > 0 + +For a full list of built-in conditions, see :mod:`~marionette_driver.expected`. |