Bug 1097889 - [Settings] The user feedback textbox resets if the screen ...

...is locked
You could define a mock of the `feedback_send` module with `sendFeedback` stubbed. You could refer to this file [1] for details.

[1]: https://github.com/mozilla-b2g/gaia/blob/master/apps/settings/test/unit/modules/apn/apn_list_test.js#L10