--- /dev/null
+<?php
+
+namespace Drupal\Tests\drupalmoduleupgrader\Unit\Plugin\DMU\Fixer;
+
+use Drupal\drupalmoduleupgrader\Plugin\DMU\Fixer\Define;
+use Drupal\Tests\drupalmoduleupgrader\Unit\TestBase;
+
+/**
+ * @group DMU.Fixer
+ */
+class DefineTest extends TestBase {
+
+ public function test() {
+ $config = [
+ 'key' => 'foo.settings/baz',
+ 'value' => 'wambooli',
+ 'in' => '~/foo.settings.yml',
+ ];
+ $plugin = new Define($config, uniqID(), []);
+ $plugin->setTarget($this->target);
+ $plugin->execute();
+
+ $url = $this->dir->getChild('foo.settings.yml')->url();
+ $this->assertFileExists($url);
+ $expected = <<<END
+foo.settings:
+ baz: wambooli
+
+END;
+ $this->assertEquals($expected, file_get_contents($url));
+ }
+
+}