1. Install PHPUnit by following their installation guide. If you've installed it correctly, this should display the version:

   $ phpunit --version

2. Install WordPress and the WP Unit Test lib using the install.sh script. Change to the plugin root directory and type:

   $ tests/bin/install.sh [db-host]

Sample usage:

$ tests/bin/install.sh woocommerce_tests root root

Important: The <db-name> database will be created if it doesn't exist and all data will be removed during testing.

Simply change to the plugin root directory and type:

$ phpunit

The tests will execute and you'll be presented with a summary. Code coverage documentation is automatically generated as HTML in the tmp/coverage directory.

You can run specific tests by providing the path and filename to the test class:

$ phpunit tests/unit-tests/api/webhooks

A text code coverage summary can be displayed using the --coverage-text option:

$ phpunit --coverage-text

• Each test file should roughly correspond to an associated source file, e.g. the formatting/functions.php test file covers code in the wc-formatting-functions.php file
• Each test method should cover a single method or function with one or more assertions
• A single method or function can have multiple associated test methods if it's a large or complex method
• Use the test coverage HTML report (under tmp/coverage/index.html) to examine which lines your tests are covering and aim for 100% coverage
• For code that cannot be tested (e.g. they require a certain PHP version), you can exclude them from coverage using a comment: // @codeCoverageIgnoreStart and // @codeCoverageIgnoreEnd. For example, see wc_round_tax_total()
• In addition to covering each line of a method/function, make sure to test common input and edge cases.
• Prefer assertsEquals() where possible as it tests both type & equality
• Remember that only methods prefixed with test will be run so use helper methods liberally to keep test methods small and reduce code duplication. If there is a common helper method used in multiple test files, consider adding it to the WC_Unit_Test_Case class so it can be shared by all test cases
• Filters persist between test cases so be sure to remove them in your test method or in the tearDown() method.
• Use data providers where possible. Be sure that their name is like data_provider_function_to_test (i.e. the data provider for test_is_postcode would be data_provider_test_is_postcode). Read more about data providers here.

Tests are automatically run with Travis-CI for each commit and pull request.

Code coverage is available on Coveralls which receives updated data after each Travis build.