Updating tests

[Janther]

This update gets our testing framework closer to what's needed when prettier v3 releases so changes when we start supporting v3 will be minimal.

Main changes are:

• have 1 test with multiple expect per snapshot instead of 1 test per expect per snapshot.
• now Prettier format functions are wrapped with an await (v3 returns promises and v2 won't bother)
• updating tests dependencies