Migrate to new testing library

[thekid]

See xp-framework/rfc#344 and https://github.com/xp-framework/test. Mostly migrated automatically, needed to add missing annotation imports in various places.

Timing

Before

Tests:       61 passed
Memory used: 5722.86 kB (5775.77 kB peak)
Time taken:  0.147 seconds

After

Test cases:  61 succeeded
Memory used: 5591.96 kB (5646.14 kB peak)
Time taken:  0.163 seconds (0.555 seconds overall)