How to Setup Testing of Modules and Themes

In order for unit testing to work with a module or a theme, you must add the module or theme's composer.json file to test/composers.json and run composer install --lock from the test directory.

Quick Start

1. When you see tests/composer.json, we are referring the file included in the dist folder of this project, which is the root directory containing the test runner phpunit.xml.
2. Create composer.json in the module's folder ensuring it will autoload the module's classes that will be tested. If not testing classes, but functions, make sure the module's composer.json file loads all files that contain the functions to be tested, usually using requre-dev. This file may or may not have anything to do with Drupal (depending on the module's implementation), but it is required by the test runner's unit testing strategy.
3. Add the path to the test runner's composer.json to tests/composer.json, and you must call composer update --lock on the test runner for dependencies to be installed for the test runner.
4. Add one or more tests to the module (according the file structure convention) extending one of the abstract classes provided by this module, e.g. \AKlump\DrupalTest\UnitTestBase, `

Test File Structure

Each module or theme provides tests and schema files relative to it's own directory (.). Following this convention allows the test runner to auto-discover these tests. e.g.,

.
└── tests
    ├── jsonschema
    │   └── story_resource.json
    └── src
        ├── Client
        │   ├── Service
        │   │   └── EarthriseServiceClientTest.php
        ├── Kernel
        │   ├── Service
        │   │   ├── BreakpointServiceKernelTest.php
        │   └── TransformKernelTest.php
        ├── TestBase.php
        └── Unit
            ├── Service
            │   └── EarthriseServiceUnitTest.php
            └── TransformUnitTest.php

Add the Module's composer.json

For a module to be unit testable it must have a composer.json file, which autoloads it's classes, the path of which must be added to this project's composer.json file, in the section extra.merge-plugin.require. This is how the unit tests are able to autoload classes without bootstrapping Drupal, e.g.,

    "extra": {
        "merge-plugin": {
            "require": [
                "../web/sites/all/modules/custom/gop3_core/composer.json"
            ]
        }
    }

Add the module file as an autoload file

If you are unit testing a module that does not use classes, but functions and it has no dependencies, you do not need to add it's composer.json file to projects composer.json. Instead you can tell this project to autoload the module files that have the functions you need to test, e.g.

    "autoload-dev": {
        "files": [
            "../web/sites/all/modules/custom/twiggy/twiggy.module"
        ]
    },        

Must Test Classes Test a Single Class?

Unit and Kernel tests do not have to test a single class, for example if you are writing a test to cover theme functions. In order to make this happen you have to do the following in your test class:

    class InTheLoftThemeKernelTest extends KernelTestBase {

      protected $schema = [

        // By setting this to false, we indicate we are not testing a class.
        'classToBeTested' => FALSE,
      ];

    ...