ComposerTest.php

<?php

namespace Drupal\Tests\Composer;

use Drupal\Composer\Composer;
use Drupal\Tests\UnitTestCase;

/**
 * @coversDefaultClass \Drupal\Composer\Composer
 * @group Composer
 */
class ComposerTest extends UnitTestCase {
    
    /**
     * Verify that Composer::ensureComposerVersion() doesn't break.
     *
     * @covers::ensureComposerVersion
     */
    public function testEnsureComposerVersion() {
        try {
            $this->assertNull(Composer::ensureComposerVersion());
        } catch (\RuntimeException $e) {
            $this->assertRegExp('/Drupal core development requires Composer 1.9.0, but Composer /', $e->getMessage());
        }
    }

}