Testing framework for office app development

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Office

Azure

Hi,

I have a requirement to develop a task pane app for office (excel, and powerpoint to be specific) which will be deployable to both Azure and desktop client.

I also have to be able to set up integration testing framework for this app.

Given that information I have two questions going through my mind that you might be able to help me with.

If I were to test the online app ( e.g using Selenium in I.E ) could I guarantee same behaviour in the desktop version? Does the JavaScript api behave the same way on desktop and online?
Secondly, what is the testing framework that would be preferred in this scenario?
Thank you for your help