There's a saying in nursing: "If it's wet, dry it. It it's dry, wet it."

I think we need the same thing in programming.

If it's slow, make it faster. If it's unreadable, make it readable. If it's coupled, decouple it.

Then just stop worrying if we fall into official definitions of unit, integration, collaborator, mock, stub, double, etc. I swear we spend more time as an industry arguing about that stuff than actually writing code, myself included.