trait ExternalCommandRequirementsTrait

trait ExternalCommandRequirementsTrait {
    
    /**
     * A list of existing external commands we've already discovered.
     *
     * @var string[]
     */
    private static $existingCommands = [];
    
    /**
     * Checks whether required external commands are available per test class.
     *
     * @throws \PHPUnit\Framework\SkippedTestError
     *   Thrown when the requirements are not met, and this test should be
     *   skipped. Callers should not catch this exception.
     */
    private static function checkClassCommandRequirements() {
        $annotations = Test::parseTestMethodAnnotations(static::class);
        if (!empty($annotations['class']['requires'])) {
            static::checkExternalCommandRequirements($annotations['class']['requires']);
        }
    }
    
    /**
     * Checks whether required external commands are available per method.
     *
     * @throws \PHPUnit\Framework\SkippedTestError
     *   Thrown when the requirements are not met, and this test should be
     *   skipped. Callers should not catch this exception.
     */
    private static function checkMethodCommandRequirements($name) {
        $annotations = Test::parseTestMethodAnnotations(static::class, $name);
        if (!empty($annotations['method']['requires'])) {
            static::checkExternalCommandRequirements($annotations['method']['requires']);
        }
    }
    
    /**
     * Checks missing external command requirements.
     *
     * @param string[] $annotations
     *   A list of requires annotations from either a method or class annotation.
     *
     * @throws \PHPUnit\Framework\SkippedTestError
     *   Thrown when the requirements are not met, and this test should be
     *   skipped. Callers should not catch this exception.
     */
    private static function checkExternalCommandRequirements(array $annotations) {
        // Make a list of required commands.
        $required_commands = [];
        foreach ($annotations as $requirement) {
            if (strpos($requirement, 'externalCommand ') === 0) {
                $command = trim(str_replace('externalCommand ', '', $requirement));
                // Use named keys to avoid duplicates.
                $required_commands[$command] = $command;
            }
        }
        // Figure out which commands are not available.
        $unavailable = [];
        foreach ($required_commands as $required_command) {
            if (!in_array($required_command, self::$existingCommands)) {
                if (static::externalCommandIsAvailable($required_command)) {
                    // Cache existing commands so we don't have to ask again.
                    self::$existingCommands[] = $required_command;
                }
                else {
                    $unavailable[] = $required_command;
                }
            }
        }
        // Skip the test if there were some we couldn't find.
        if (!empty($unavailable)) {
            throw new SkippedTestError('Required external commands: ' . implode(', ', $unavailable));
        }
    }
    
    /**
     * Determine if an external command is available.
     *
     * @param $command
     *   The external command.
     *
     * @return bool
     *   TRUE if external command is available, else FALSE.
     */
    private static function externalCommandIsAvailable($command) {
        $finder = new ExecutableFinder();
        return (bool) $finder->find($command);
    }

}