Fix this issue and add test

Author: SOHELAHMED7

src/spec/OpenApi.php

@@ -7,7 +7,6 @@
 
 namespace cebe\openapi\spec;
 
-use cebe\openapi\exceptions\TypeErrorException;
 use cebe\openapi\SpecBaseObject;
 
 /**
@@ -79,11 +78,11 @@ public function performValidation()
             $this->addError('Unsupported openapi version: ' . $this->openapi);
         }
 
-        $providedFields = array_keys(json_decode(json_encode($this->getSerializableData()), true)); # TODO this getSerializableData() can be eliminated if  
+        $providedFields = array_keys($this->getRawSpecData());
         $allowedFields = array_keys($this->attributes());
         foreach ($providedFields as $field) {
             if (!in_array($field, $allowedFields)) {
-                $this->addError('Invalid top level fields: ' . $field);
+                $this->addError('Invalid top level field: "' . $field . '". More information can be obtained at https://spec.openapis.org/oas/v3.0.3.html#fixed-fields');
             }
         }
     }

tests/spec/OpenApiTest.php

@@ -236,7 +236,7 @@ public function testSpecs($openApiFile)
     public function testInvalidTopLevelField()
     {
         $openapi = new OpenApi([
-            'AAcomponents' => [
+            'AAAAAcomponents' => [
                 'User' => [
                     'type' => 'object',
                     'properties' => [
@@ -247,12 +247,12 @@ public function testInvalidTopLevelField()
                 ]
             ]
         ]);
-        $isValid = $openapi->validate();
-//        $this->assertTrue($openapi->validate());
+        $this->assertFalse($openapi->validate());
         $this->assertEquals([
             'OpenApi is missing required property: openapi',
             'OpenApi is missing required property: info',
             'OpenApi is missing required property: paths',
+            'Invalid top level field: "AAAAAcomponents". More information can be obtained at https://spec.openapis.org/oas/v3.0.3.html#fixed-fields',
         ], $openapi->getErrors());
 
 //        // check default value of servers