Remove else statement that causes schemas to not be set correctly

[survivorbat]

Did a few. things, with the removal of the else being the main update.

• Make tests run in parallel
• Rename unexported mock properties to better reflect purpose (they aren't caches)
• Fix existing schemas not loading if a version is given in SetSchema

If you're not interested in the rename or parallel I can remove those changes

[survivorbat]

Hey @riferrei, if you find time could you perhaps have a look at this change? :)

[survivorbat]

Another improvement: Makes sure Codec's error is returned

[AtakanColak]

Thanks @survivorbat!