test ordered element queries

backend/tests/Feature/Element/EloquentElementRepositoryTest.php

@@ -97,6 +97,65 @@ class EloquentElementRepositoryTest extends TestCase
         ));
     }
 
+    public function testItListsOrderedElementsWithinTheirTreeScope(): void
+    {
+        $bible = $this->createSet('Bible');
+        $course = $this->createSet('Course');
+        $repository = app(ElementRepository::class);
+        $genesisBook = $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Genesis',
+            kind: 'book',
+            parentElement: null,
+        ));
+        $exodusBook = $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Exodus',
+            kind: 'book',
+            parentElement: null,
+        ));
+        $repository->create(new CreateElementDto(
+            set: $course,
+            name: 'Module 1',
+            kind: 'module',
+            parentElement: null,
+        ));
+        $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Genesis',
+            kind: 'portion',
+            parentElement: $genesisBook,
+        ));
+        $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Noah',
+            kind: 'portion',
+            parentElement: $genesisBook,
+        ));
+        $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Shemot',
+            kind: 'portion',
+            parentElement: $exodusBook,
+        ));
+
+        $topLevelElements = $repository->findTopLevelBySet($bible);
+        $childElements = $repository->findByParentElement($genesisBook);
+
+        $this->assertSame(
+            ['Genesis', 'Exodus'],
+            array_map(function ($element): string {
+                return $element->getName();
+            }, $topLevelElements),
+        );
+        $this->assertSame(
+            ['Genesis', 'Noah'],
+            array_map(function ($element): string {
+                return $element->getName();
+            }, $childElements),
+        );
+    }
+
     private function createSet(string $name): Set
     {
         $creator = app(UserRepository::class)->create(new CreateUserDto(