Add a verification flag which checks formatter behaviour

[brianmcgee]

Is your feature request related to a problem? Please describe.

Some formatters don't always work as expected, perhaps out of the box (requiring some flags) or have a bug. With a non-trivial setup, as seen in #342, it can be difficult to diagnose which formatter is responsible.

Describe the solution you'd like

Some form of enhanced checking of formatter behaviour which can be toggled via a cli flag.