Initial pass at fixing the tests #24
Description
After we ported the tests, there will probably be many failures, but that's ok as this is test-driven development.
Probably we can fix most tests by porting the code, then are left with some tests either failing because of small differences in test methodology (React Helmet uses some React test tools that don't translate well (or at least I dont know how) to Preact). This issue should fix most tests but it's ok if a bunch are left failing.
We will fix those last tests one by one or maybe even get rid of them if we think it's safe.