Copying from another post I did here on the Club, which was improved by @robertmeaney on Twitter :
Testing: The act of learning about a product through experimentation and exploration.
Testability: The capacity of the product to ease the process of learning, both on the “input” (act on the product) and on the “output” (understanding how to the product responded) - in the context of the environment and testers themselves*.
- Silly example: If all logs are in Portuguese, the logs only improve testability to Portuguese-speaking people.