docs: Add documentation regarding raven-teskit plugin (#1231)
docs: Add documentation regarding raven-teskit plugin (#1231)

* handle case where both stackstraces are undefined when checking 'isSameException'
* add documentation regarding raven-teskit plugin
* adding raven-testkit docs to Tips and Tricks

getsentry/raven-js,getsentry/raven-js,getsentry/raven-js,getsentry/raven-js