This guide will demonstrate how to:

• set up unit tests for an existing plugin, using WP-CLI
• run the tests locally

We're going to assume that you already have a plugin called my-plugin.

So, let's get started:

1. Install PHPUnit (4.8.x required, 5.x not supported).

2. Generate the plugin test files:

   wp scaffold plugin-tests my-plugin

This command will generate all the files needed for running tests, including a .travis.yml file. If you host your plugin on Github and enable Travis CI, the tests will be run automatically after every commit you make to the plugin.

3. Initialize the testing environment locally:

(you'll need to already have svn and wget available)

cd $(wp plugin path my-plugin --dir)
bash bin/install-wp-tests.sh wordpress_test root '' localhost latest

where:

• wordpress_test is the name of the test database (all data will be deleted!)
• root is the MySQL user name
• '' is the MySQL user password
• localhost is the MySQL server host
• latest is the WordPress version; could also be 3.7, 3.6.2 etc.

This script does a couple things. First it installs a copy of WordPress in the tmp/ directory (by default) as well as the WordPress unit testing tools. Then it creates a database to be used while running tests.

NOTE: This script can be run multiple times without errors, but it will not overwrite previously existing files. So if your DB credentials change, or you want to switch to a different instance of mysql, simply re-running the script won't be enough. You'll need to manually edit the wp-config.php that's installed in the tmp/.

4. Run the plugin tests:

   phpunit

Note: phpunit 4.8.x is required (5.x won't work)