Currently -v controls both terminal verbosity (how to display test session progress in the terminal) and diff verbosity (how verbose is our diffs when assertions fail).

I've often wanted to increase diff verbosity while also keeping terminal verbosity at the normal level, but this is not possible today.

Proposal

Introduce a new option that controls only diff verbosity (for discussion here -dv, but please let's bikeshed on this).

For backward compatibility reasons, -v keeps controlling both terminal verbosity and diff verbosity, but -dv can be used to increase diff verbosity independently.

• -v: when used, increase both terminal verbosity and diff verbosity.
• -dv: when used, increase diff verbosity only (we also need the equivalent of -q for diff verbosity).

With -dv in place, we might even consider changing to a higher level of diff verbosity in the future by default, but that remains to be seen.

Related: #6292, #5192