Micro black holes grow to become filaments of dark matter density.
For this to happen gravity needs to have density.

So all gravitation effects would need to have a crossover point.
For matter it is iron - the neutral between fusion and fission.
For magnetism the strength of the field.

This is where the simplest test comes in.
Two magnets should require slightly less force to hold same poles together than slightly apart.

For black holes there should be a zero point, I can only guess in our current gravity density it would be if the matter within is the size of a small mountain and that is by using mainsteam calculations.

Large black holes should give off large amounts of Hawkin's radiation and very small holes (the energy of a garden pea for instance).

The mountain size black hole should be the cross over point and given the right access to matter continue to grow or dissolve very slowly.

Cheers Mike