Search: add tests for XSS

[stsewd]

In 33989f1 we fixed a XSS vulnerability, we should have tests for it, so it doesn't happen again.

[humitos]

I tried to quickly write this test but it's not easy. We don't have any test currently for the search addon and they are not trivial to write. I will need to spend some time working on the initial test pattern for this addon before being able to write this particular test case.