test: add toObject equivalence tests against json_encode/json_decode

Verify that the toObject() helper produces structurally identical output
to json_decode(json_encode()) across 17 edge cases: scalars, empty arrays,
sequential/associative arrays, non-sequential integer keys, deeply nested
structures, and mixed types.

Author: wadakatu

tests/Unit/OpenApiResponseValidatorTest.php

@@ -4,14 +4,19 @@
 
 namespace Studio\OpenApiContractTesting\Tests\Unit;
 
+use const JSON_THROW_ON_ERROR;
+
 use InvalidArgumentException;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
+use ReflectionMethod;
 use Studio\OpenApiContractTesting\OpenApiResponseValidator;
 use Studio\OpenApiContractTesting\OpenApiSpecLoader;
 
 use function array_map;
 use function count;
+use function json_encode;
 use function range;
 
 class OpenApiResponseValidatorTest extends TestCase
@@ -32,6 +37,42 @@ protected function tearDown(): void
         parent::tearDown();
     }
 
+    // ========================================
+    // toObject equivalence tests
+    // ========================================
+
+    /**
+     * @return iterable<string, array{mixed}>
+     */
+    public static function provideTo_object_matches_json_roundtripCases(): iterable
+    {
+        yield 'null' => [null];
+        yield 'string' => ['hello'];
+        yield 'integer' => [42];
+        yield 'float' => [3.14];
+        yield 'boolean true' => [true];
+        yield 'boolean false' => [false];
+        yield 'empty array' => [[]];
+        yield 'sequential array' => [[1, 2, 3]];
+        yield 'associative array' => [['key' => 'value', 'num' => 1]];
+        yield 'nested associative' => [['a' => ['b' => ['c' => 'deep']]]];
+        yield 'list of objects' => [[['id' => 1, 'name' => 'a'], ['id' => 2, 'name' => 'b']]];
+        yield 'non-sequential int keys' => [[1 => 'a', 3 => 'b']];
+        yield 'mixed nested' => [
+            [
+                'users' => [
+                    ['id' => 1, 'tags' => ['admin', 'user'], 'meta' => ['active' => true]],
+                ],
+                'total' => 1,
+                'filters' => [],
+            ],
+        ];
+        yield 'numeric string keys' => [['200' => ['description' => 'OK']]];
+        yield 'deeply nested list' => [[[['a']]]];
+        yield 'null in array' => [[null, 'a', null]];
+        yield 'empty nested object' => [['data' => []]];
+    }
+
     // ========================================
     // OAS 3.0 tests
     // ========================================
@@ -744,4 +785,20 @@ public function v30_strip_prefixes_applied(): void
         $this->assertTrue($result->isValid());
         $this->assertSame('/v1/pets', $result->matchedPath());
     }
+
+    #[Test]
+    #[DataProvider('provideTo_object_matches_json_roundtripCases')]
+    public function to_object_matches_json_roundtrip(mixed $input): void
+    {
+        $method = new ReflectionMethod(OpenApiResponseValidator::class, 'toObject');
+
+        $actual = $method->invoke(null, $input);
+
+        // Re-encode both to JSON to compare structural equivalence
+        // without relying on object identity (assertSame fails on stdClass).
+        $expectedJson = json_encode($input, JSON_THROW_ON_ERROR);
+        $actualJson = (string) json_encode($actual, JSON_THROW_ON_ERROR);
+
+        $this->assertSame($expectedJson, $actualJson);
+    }
 }