WordPress testing (core) is useful when contributing to the WordPress core. The first thing you have to do is install PHPUnit 7 (8 doesn't work with WordPress yet).

In your terminal, run

curl https://phar.phpunit.de/phpunit.phar -L -o phpunit.phar
chmod +x phpunit.phar
mv phpunit.phar /usr/local/bin/phpunit

You can also run

brew install phpunit
chmod +x phpunit.phar
mv phpunit.phar /usr/local/bin/phpunit

Then check the test repository. WordPress tests live in the core development repository, available via SVN at:

svn co https://develop.svn.wordpress.org/trunk/ wordpress-develop
cd wordpress-develop

or Git:

git clone git://develop.git.wordpress.org/ wordpress-develop
cd wordpress-develop

Create an empty MySQL database. Be careful not to use an existing project database, as the test suite will delete all data from the designated database.

Set up a config file. Copy wp-tests-config-sample.php to wp-tests-config.php and enter the credentials of the newly created database.

Running the test suite

To run unit tests, you need to specify the phpunit.xml.dist file. An example might look like this:

<?xml version="1.0"?>
<phpunit
  bootstrap="tests/bootstrap.php"
  backupGlobals="false"
  colors="true"
  convertErrorsToExceptions="true"
  convertNoticesToExceptions="true"
  convertWarningsToExceptions="true"
  >
  <testsuites>
    <testsuite>
      <directory prefix="test-" suffix=".php">./tests/</directory>
    </testsuite>
  </testsuites>
  <filter>
    <whitelist>
      <directory>./</directory>
      <exclude>
        <directory>./vendor</directory>
        <directory>./tests</directory>
      </exclude>
    </whitelist>
  </filter>
  <logging>
    <log type="coverage-clover" target="tests/_reports/logs/clover.xml"/>
    <log type="coverage-html" target="tests/_reports/coverage" charset="UTF-8" yui="true" highlight="true" lowUpperBound="35" highLowerBound="70" />
    <log type="testdox-text" target="tests/_reports/testdox/executed.txt"/>
    <log type="testdox-html" target="tests/_reports/testdox/testdox.html" />
  </logging>
</phpunit>

Here we've specified that code coverage should be created. For that to be done, you need to have Xdebug installed on your system. Keep in mind that Xdebug may significantly reduce the speed of your tests.

In the root directory, where wp-tests-config.php file, the tests/ folder, and the phpunit.xml.dist file are located, run:

vendor/bin/phpunit

Unit test symbol meaning

• . – Each dot signifies one “test” that passed.
• S means a test was skipped. This usually means that the test is only valid in certain configurations, such as when a test requires Multisite.
• F means a test failed. More output on what exactly failed and where will be shown.
• E means a test failed because of a PHP error, warning, or notice.
• I means a test was marked as incomplete.

Testing inside VVV

VVV comes with a test-ready environment wordpress-develop/, where you can test various patches. It already has the test suite set up so you don't need to do anything manually.

Once you are in the wordpress-develop/public_html/ folder, run

npm install

Then run

npm install -g grunt-cli

After grunt-cli has been installed, run

grunt build

If the build fails on the node-sass package, try rebuilding it again.

npm rebuild node-sass

Note: The build process is currently under revision (https://core.trac.wordpress.org/ticket/43055?cversion=0&cnum_hist=23).

Applying a patch

Make sure that VVV is running and the above steps have been completed. You can then ssh to Vagrant, go to the wordpress-develop/public_html/ folder and run

grunt watch &
svn up

Now you’re ready to patch. Find a ticket with patches. This example uses #11863.

grunt patch:11863

This will show the available patches you can choose from (if there are multiple patches). After you select the patch, you can log into http://src.wordpress-develop.test/ (or http://src.wordpress-develop.test/). You can test the effects of that patch and, after you're done with it, you can revert it using

svn revert -R

or

svn revert -R --cl revertme .

You can comment on the Trac ticket with the findings or create you own patch.

Testing outside wordpress-develop

You can set up a custom clean installation of WordPress if you don't want to use the official one from VVV. In that case, just go to public_html and run

svn co https://develop.svn.wordpress.org/trunk/ .

This will download all files that are necessary for testing and patching, as described above.