For day 19 of #30daysoftesting, the challenge is:

Share a resource on testability along with your thoughts about the topic.

As a resource I want to go with something from James Bach: http://www.satisfice.com/tools/testability.pdf 

I feel that this resource covers a solid amount of what testability is about.

There are so many things to take into consideration when determining testability. Testability does not only come from the product itself. The people testing, the end-users, the organisation, the developers, similar products, the technical environment all can be taken into account when it comes to the testability. Following best (or good)practices in work goes a long way to improving products’ testability, for example when it comes to writing clean code, good unit tests, solid documentation and a good testing strategy.