You may want to look at the automated functional GUI testing tool RIATest.
RIATest knows how to ignore ids dynamically generated by ExtJS, yet if you manually assign ids to the components the tool will use them for identification (see e.g. #tree2 in the sample below).
The tests in RIATest operate in terms of ExtJS UI widgets.
Examples of RIATest scripts that work with ExtJS widgets:
The following clicks on an ExtJS button with label "Next Page":
And the following does drag-n-drop of a row from one ExtJS tree to another:
And this collapses the header of an ExtJS box:
ExtTreePanel("#tree2")->ExtRow("Custom Ext JS"));
(All sample code above is from real test scripts that run on ExtJS sample applications).
(Disclaimer: I am a RIATest team member).