Update Composer, update everything

web/core/tests/Drupal/TestSite/TestSiteInstallTestScript.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Drupal\TestSite;
+
+/**
+ * Setup file used by TestSiteApplicationTest.
+ *
+ * @see \Drupal\Tests\Scripts\TestSiteApplicationTest
+ */
+class TestSiteInstallTestScript implements TestSetupInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setup() {
+    \Drupal::service('module_installer')->install(['test_page_test']);
+  }
+
+}