The code hacker as originally designed, as a mechanism that allowed
to enable hacks at the individual test level, is flawed because it
assumes that code files are loaded before each test, but actually
the PHP engine loads code files only once.
Therefore this commit redesigns it so that the two existing main hacks,
the functions mocker and the static methods hacker, are applied
to all the relevant functions and classes at bootstrap time, and
mocks for each individual function/method can be registered at the
beginning of each test. See README for the full details.
The testing tools (only the code hacker at this time) have been moved
from 'src' to 'tests/Tools', since many opcode cache plugins
load the whole src folder in production.
Also, an extra autoloader is set in the tests bootstrap so that
the 'tests/Tools' directory corresponds, using PSR4, to the
'Automattic\WooCommerce\Testing\Tools' namespace.
Nestor Soriano