feat: build the questionnaire form from its definition

tests/Model/Questionnaire/DefinitionTest.php

@@ -44,6 +44,22 @@ class DefinitionTest extends TestCase
         $this->assertFalse($definition->isVisible($details, ['damage' => 'no', 'claim' => 'expected']));
     }
 
+    public function testWithoutHiddenAnswersDropsHiddenEmptyAndUnknownAnswers(): void
+    {
+        $answers = [
+            'damage' => 'no',
+            'claim' => 'expected',      // hidden now that damage is "no"
+            'details' => 'Spiegel ab',  // hidden in turn
+            'unknown' => 'x',           // not a question of this definition
+        ];
+
+        $this->assertSame(['damage' => 'no'], $this->definition()->withoutHiddenAnswers($answers));
+        $this->assertSame(
+            ['damage' => 'yes', 'claim' => 'settled'],
+            $this->definition()->withoutHiddenAnswers(['damage' => 'yes', 'claim' => 'settled', 'details' => '']),
+        );
+    }
+
     private function definition(): Definition
     {
         $yesNo = [new Option('yes', 'Ja'), new Option('no', 'Nein')];