[BUGFIX beta] Fix link-to throwing in integration tests

Fixes #15831

Fixes a regression introduced by #15788 by returning early again from `routing.generateURL()` when `router._routerMicrolib` is not present.

(cherry picked from commit a0ace45)

packages/ember-glimmer/tests/integration/components/link-to-test.js

@@ -1,4 +1,4 @@
-import { moduleFor, ApplicationTest } from '../../utils/test-case';
+import { moduleFor, ApplicationTest, RenderingTest } from '../../utils/test-case';
 import { Controller } from 'ember-runtime';
 import { set } from 'ember-metal';
 import { LinkComponent } from '../../utils/helpers';
@@ -156,3 +156,17 @@ moduleFor('Link-to component with query-params', class extends ApplicationTest {
     });
   }
 });
+
+moduleFor('Link-to component', class extends RenderingTest {
+  ['@test should be able to be inserted in DOM when the router is not present - block']() {
+    this.render(`{{#link-to 'index'}}Go to Index{{/link-to}}`);
+
+    this.assertText('Go to Index');
+  }
+
+  ['@test should be able to be inserted in DOM when the router is not present - inline']() {
+    this.render(`{{link-to 'Go to Index' 'index'}}`);
+
+    this.assertText('Go to Index');
+  }
+});

packages/ember-routing/lib/services/routing.js

@@ -48,13 +48,17 @@ export default Service.extend({
   },
 
   generateURL(routeName, models, queryParams) {
+    let router = get(this, 'router');
+    // return early when the router microlib is not present, which is the case for {{link-to}} in integration tests
+    if (!router._routerMicrolib) { return; }
+
     let visibleQueryParams = {};
     if (queryParams) {
       assign(visibleQueryParams, queryParams);
       this.normalizeQueryParams(routeName, models, visibleQueryParams);
     }
 
-    return get(this, 'router').generate(routeName, ...models, { queryParams: visibleQueryParams });
+    return router.generate(routeName, ...models, { queryParams: visibleQueryParams });
   },
 
   isActiveForRoute(contexts, queryParams, routeName, routerState, isCurrentWhenSpecified) {