/**
	 * ResourceLoaderTestModules hook handler
	 * @see https://www.mediawiki.org/wiki/Manual:Hooks/ResourceLoaderTestModules
	 *
	 * @param array &$testModules
	 * @param ResourceLoader $resourceLoader
	 */
	public static function onResourceLoaderTestModules( array &$testModules,
		ResourceLoader $resourceLoader = null
	) {
		global $wgResourceModules;

		$testModuleBoilerplate = [
			'localBasePath' => dirname( __DIR__ ),
			'remoteExtPath' => 'Echo',
		];

		// find test files for every RL module
		$prefix = 'ext.echo';
		foreach ( $wgResourceModules as $key => $module ) {
			if ( substr( $key, 0, strlen( $prefix ) ) === $prefix && isset( $module['scripts'] ) ) {
				$testFiles = [];
				foreach ( $module['scripts'] as $script ) {
					$testFile = 'tests/qunit/' . dirname( $script ) . '/test_' . basename( $script );
					// if a test file exists for a given JS file, add it
					if ( file_exists( $testModuleBoilerplate['localBasePath'] . '/' . $testFile ) ) {
						$testFiles[] = $testFile;
					}
				}
				// if test files exist for given module, create a corresponding test module
				if ( $testFiles !== [] ) {
					$testModules['qunit']["$key.tests"] = $testModuleBoilerplate + [
						'dependencies' => [ $key ],
						'scripts' => $testFiles,
					];
				}
			}
		}
	}

amsa@amsa-Latitude-7480:/var/lib/mediawiki2$ php maintenance/eval.php 
> $m = [];

> $rl = new ResourceLoader( \MediaWiki\MediaWikiServices::getInstance()->getMainConfig() );

> EchoHooks::onResourceLoaderTestModules( $m, $rl );

> var_dump( $m );
array(0) {
}