How to test Office Add-ins in the online version of Word and excel?

Question

I am developing an Task Pane Office Add-in using the Office JavaScript APIs in Visual Studio. When you run the application it runs in the desktop client version of Office.

Answer 1

You can create a free 30 day trial tenant for Office 365 for testing. You'll be able to publish the Add-in, and test with an account of that tenant.
Set up a development environment for SharePoint Add-ins on Office 365

There's also the option to join Office 365 Developer Subscription program (free), and get a 1 year long trial.
http://dev.office.com/devprogram

For debugging using the Online client, you'll have to change Start Action property for your project accordingly.

Create and debug Office Add-ins in Visual Studio