GENERATORS/TESTS: Moving random generators into tests

Creating a common implementation file for tests

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Even tests functions are no longer inline

Moving the definition definition into test implementation file

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Added new random generators

These are useful for generating normalized frequencies/ranged values.
They are now used everywhere in tests.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>