The WooCommerce unit tests started failing when running using WP nightly
with the following error:
```
Fatal error: require_once(): Failed opening required '/tmp/wordpress-tests-lib/src//wp-includes/class-phpmailer.php' (include_path='.:/home/travis/.phpenv/versions/7.4.2/share/pear') in /tmp/wordpress-tests-lib/includes/mock-mailer.php on line 2
```
https://travis-ci.org/woocommerce/woocommerce/jobs/646855363#L1955
This was happening because WP changed the syntax of the line where
ABSPATH is defined in the context of the unit tests
(https://core.trac.wordpress.org/changeset/47198/trunk/wp-tests-config-sample.php)
and we rely on this syntax to change ABSPATH when running
`tests/bin/install.sh`.
To fix this problem, this commit updates the sed command used to change
ABSPATH to work when both the old and new syntaxes are used. In the
future we might want to consider a more robust solution to the problem
of updating ABSPATH.
This commit changes the regular expression used to determine the WP_TESTS_TAG variable to ignore WP beta releases otherwise install_test_suite() will fail to download the test suite. This is part of workaround to run WooCommerce unit tests using PHP 7.3 and WP 5.0 beta-5.
Rodrigo Primo
Julia Amosova
Gerhard
Ian Jenkins
Galen Wright-Watson
Brent Sessions
Brent Sessions
Mike Jolley
Claudio Sanches
Jeff Stieler
Barry Kooij
Max Rice