Relative path used in test suite forces tests to be ran from tests dir

[PressLabs]

In the wordPress test suite for version 4.7.3, inside tests/phpunit/tests/rest-api/rest-schema-setup.php line 303 a relative path is used for writing into a file.
Our use case is that the WordPress tests are cloned into our project and they run alongside our own test suite from an upper level directory in an automated build. That makes this specific test to fail since it cannot resolve the relative path correctly and thus the whole build fails.

The suggestion would be to use absolute paths here in order to let others include this test suite as a subset of a bigger test suite and run all of them from top level, without cd-ing into every subset.

[johnbillion]

Thanks for the report @PressLabs. Could you give 40071.diff​ a test and see if it addresses the issue for you?

Introduced in [40058].

[johnbillion]

cc @adamsilverstein for sanity check.

[adamsilverstein]

Replying to johnbillion:

cc @adamsilverstein for sanity check.

@johnbillion Looks good. I tested this out and verified the fixture file is generated in the correct location when I run phpunit from the root.

[PressLabs]

I confirm that the fix works.

[adamsilverstein]

In 42741:

Unit Tests: add a DIR_TESTROOT constant to avoid relative paths.

Fix an issue that prevents tests from running correctly when run outside their normal context.

Props PressLabs, johnbillion.
Fixes #40071.