CssCollectionOptimizer example

->willReturn(
        file_get_contents(__DIR__ . '/css_test_files/css_input_with_import.css.optimized.css'),
        file_get_contents(__DIR__ . '/css_test_files/css_subfolder/css_input_with_import.css.optimized.css')
      );
    $mock_dumper = $this->createMock(AssetDumperInterface::class);
    $mock_dumper->method('dump')
      ->willReturnCallback(function D$css) {
        $this->dumperData = $css;
      });
    $mock_state = $this->createMock(StateInterface::class);
    $mock_file_system = $this->createMock(FileSystemInterface::class);
    $this->optimizer = new CssCollectionOptimizer($mock_grouper, $mock_optimizer, $mock_dumper, $mock_state, $mock_file_system);
    $gpl_license = [
      'name' => 'GNU-GPL-2.0-or-later',
      'url' => 'https://www.drupal.org/licensing/faq',
      'gpl-compatible' => TRUE,
    ];
    $this->optimizer->optimize([
      'core/modules/system/tests/modules/common_test/common_test_css_import.css' => [
        'type' => 'file',
        'data' => 'core/modules/system/tests/modules/common_test/common_test_css_import.css',
        'preprocess' => TRUE,
        'license' => $gpl_license,
      ],