Formatting guidelines are not shown for textareas without WYSIWYG

The class name was incorrect. JavaScript was not able to show the selected guideline.

diff --git a/core/themes/classy/templates/filter/filter-guidelines.html.twig b/core/themes/classy/templates/filter/filter-guidelines.html.twig
index 783992b..9459c1a 100644
--- a/core/themes/classy/templates/filter/filter-guidelines.html.twig
+++ b/core/themes/classy/templates/filter/filter-guidelines.html.twig
@@ -22,7 +22,7 @@
...
-    'filter-guidelines-' ~ format.format,
+    'filter-guidelines-' ~ format.id,

There was a funy situation. Renderer set #access to false, so few guidelines were not rendered.
I added a prefix. It works well.

diff --git a/core/modules/filter/src/Element/TextFormat.php b/core/modules/filter/src/Element/TextFormat.php
index aaff8b4..4b213d8 100644
--- a/core/modules/filter/src/Element/TextFormat.php
+++ b/core/modules/filter/src/Element/TextFormat.php
@@ -161,7 +161,7 @@ public static function processFormat(&$element, FormStateInterface $form_state,
...
-      $element['format']['guidelines'][$format->id()] = array(
+      $element['format']['guidelines']['format-' . $format->id()] = array(

Added test cases to check if guidelines were rendered.

diff --git a/core/modules/filter/src/Tests/TextFormatElementFormTest.php b/core/modules/filter/src/Tests/TextFormatElementFormTest.php
index b889c4a..2851e34 100644
--- a/core/modules/filter/src/Tests/TextFormatElementFormTest.php
+++ b/core/modules/filter/src/Tests/TextFormatElementFormTest.php
@@ -117,10 +117,16 @@ public function testTextFormatElement() {
+    // It tests if guidelines are included.
...
+    $this->assertRaw('filter-guidelines-full_html');
+    $this->assertRaw('filter-guidelines-filtered_html');
+    $this->assertRaw('filter-guidelines-filter_test');

Also moved filter twig templates from classy theme to the module to make the site and tests working the same.

The idea has been born: Let's move renderer items instead the twig templates he in the filter module. It will look more simple and standart.

Because templates were copiedd to the module folder, extra classes appeared.

-    $expected = '<figure><img src="llama.jpg" /><figcaption>Loquacious llama!</figcaption></figure>';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption>Loquacious llama!</figcaption></figure>';

@idebr Yes, I saw the issue. It seems I do not understand the purpose of the theme classy. I see that theme - bartik reuses the classy. Tests use module templates. So I copied templates from classy to the module and corrected tests. Advise me how to correct templates right to make tests workable.

There is an idea to move "guidelines" from templates to renderable array. It will look more clear and common.