Ensures a theme's .info.yml file is able to override a module CSS file from being added to the page.
function testCSSOverride() {
// Reuse the same page as in testPreprocessForSuggestions(). We're testing
// what is output to the HTML HEAD based on what is in a theme's .info.yml
// file, so it doesn't matter what page we get, as long as it is themed with
// the test theme. First we test with CSS aggregation disabled.
$config = config('system.performance');
$config
->set('css.preprocess', 0);
$config
->save();
$this
->drupalGet('theme-test/suggestion');
$this
->assertNoText('system.module.css', 'The theme\'s .info.yml file is able to override a module CSS file from being added to the page.');
// Also test with aggregation enabled, simply ensuring no PHP errors are
// triggered during drupal_build_css_cache() when a source file doesn't
// exist. Then allow remaining tests to continue with aggregation disabled
// by default.
$config
->set('css.preprocess', 1);
$config
->save();
$this
->drupalGet('theme-test/suggestion');
$config
->set('css.preprocess', 0);
$config
->save();
}