Add a test case covering rendering a custom loading template

Author: jakubtobiasz

src/LiveComponent/tests/Fixtures/templates/dummy/loading.html.twig

@@ -0,0 +1 @@
+I'm loading a reaaaally slow live component

src/LiveComponent/tests/Fixtures/templates/render_deferred_component_with_template.html.twig

@@ -0,0 +1 @@
+<twig:deferred_component defer defer-loading-template='dummy/loading.html.twig' />

src/LiveComponent/tests/Functional/EventListener/AddLiveAttributesSubscriberTest.php

@@ -145,10 +145,10 @@ public function testItSetsDeferredTemplateIfLiveIdNotPassed(): void
             ->filter('div')
         ;
 
-        $this->assertSame('', $div->html());
+        $this->assertSame('', trim($div->html()));
+        $this->assertSame('live:connect->live#$render', $div->attr('data-action'));
 
         $component = $this->mountComponent('deferred_component', [
-            'defer' => false,
             'data-live-id' => $div->attr('data-live-id'),
         ]);
 
@@ -163,4 +163,31 @@ public function testItSetsDeferredTemplateIfLiveIdNotPassed(): void
 
         $this->assertSame('Long awaited data', $div->html());
     }
+
+    public function testItIncludesGivenTemplateWhileLoadingDeferredComponent(): void
+    {
+        $div = $this->browser()
+            ->visit('/render-template/render_deferred_component_with_template')
+            ->assertSuccessful()
+            ->crawler()
+            ->filter('div')
+        ;
+
+        $this->assertSame('I\'m loading a reaaaally slow live component', trim($div->html()));
+
+        $component = $this->mountComponent('deferred_component', [
+            'data-live-id' => $div->attr('data-live-id'),
+        ]);
+
+        $dehydrated = $this->dehydrateComponent($component);
+
+        $div = $this->browser()
+            ->visit('/_components/deferred_component?props=' . urlencode(json_encode($dehydrated->getProps())))
+            ->assertSuccessful()
+            ->crawler()
+            ->filter('div')
+        ;
+
+        $this->assertStringContainsString('Long awaited data', $div->html());
+    }
 }