diff options
| author | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
|---|---|---|
| committer | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
| commit | 5f8de423f190bbb79a62f804151bc24824fa32d8 (patch) | |
| tree | 10027f336435511475e392454359edea8e25895d /testing/marionette/client/docs/advanced/stale.rst | |
| parent | 49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff) | |
| download | UXP-5f8de423f190bbb79a62f804151bc24824fa32d8.tar UXP-5f8de423f190bbb79a62f804151bc24824fa32d8.tar.gz UXP-5f8de423f190bbb79a62f804151bc24824fa32d8.tar.lz UXP-5f8de423f190bbb79a62f804151bc24824fa32d8.tar.xz UXP-5f8de423f190bbb79a62f804151bc24824fa32d8.zip | |
Add m-esr52 at 52.6.0
Diffstat (limited to 'testing/marionette/client/docs/advanced/stale.rst')
| -rw-r--r-- | testing/marionette/client/docs/advanced/stale.rst | 71 |
1 files changed, 71 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 000000000..0af576865 --- /dev/null +++ b/testing/marionette/client/docs/advanced/stale.rst @@ -0,0 +1,71 @@ +Dealing with Stale Elements +=========================== +.. py:currentmodule:: 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 +---------------------------------------- + +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:: + + 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:: + + 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.expected`. |