pr suggestions around test validation

tests/ArrayBasedFormatterTestCases.php

@@ -465,6 +465,14 @@ public function value_objects_with_similar_property_names_work_validate(mixed $s
         self::assertSame('me@example.com', $toTest['email']);
     }
 
+    public function nullable_value_objects_flattened_validate(mixed $serialized): void
+    {
+        $toTest = $this->arrayify($serialized);
+
+        self::assertTrue(isset($toTest['order_id']));
+        self::assertNull($toTest['order_id']);
+    }
+
     public function multiple_same_class_value_objects_work_validate(mixed $serialized): void
     {
         $toTest = $this->arrayify($serialized);

tests/SerdeTestCases.php

@@ -1630,21 +1630,21 @@ public function nullable_value_objects_flattened(): void
 
         $data = new FlattenedValueObjectMain(null);
 
-        // Serialisation here hides the issue...
-        // $serialized = $s->serialize($data, $this->format);
+        $serialized = $s->serialize($data, $this->format);
 
-        $serialized = match ($this->format) {
-            'array' => ['order_id' => null],
-            'json' => '{"order_id":null}',
-            'yaml' => 'order_id: null',
-        };
+        $this->nullable_value_objects_flattened_validate($serialized);
 
         /** @var FlattenedNullableMain $result */
         $result = $s->deserialize($serialized, from: $this->format, to: $data::class);
 
         self::assertEquals($data, $result);
     }
 
+    public function nullable_value_objects_flattened_validate(mixed $serialized): void
+    {
+
+    }
+
     #[Test]
     public function non_sequence_arrays_are_normalized_to_sequences(): void
     {