test(assertions): Simplify assertResultErrors to avoid closure serialization (drupal-graphql#1159)

This commit changes some loops into built-in PHP functions to simplify
the code and eliminate the need for closures.

Additionally this switches over to an `assertEmpty` from `assertEquals`.
This achieves the same test result and in the message still provides the
errors. However it prevents test failures with weird serialization
complaints that are caused by closures in function arguments of GraphQL
Error stacktraces. See sebastianbergmann/phpunit#4371 (comment)

The downside to this change is that we may lose some contextual
information that the full error in the array comparison may provide. The
upside is that we can actually see why tests fail since in a lot of
cases this beneficial diff doesn't make it into the test output anyway.
So all-in-all this is a step forward.

Author: Kingdutch

tests/src/Traits/QueryResultAssertionTrait.php

@@ -4,7 +4,6 @@
 
 use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\graphql\GraphQL\Execution\ExecutionResult;
-use GraphQL\Error\Error;
 use GraphQL\Server\OperationParams;
 
 /**
@@ -145,34 +144,28 @@ private function assertResultData(ExecutionResult $result, $expected): void {
    * @internal
    */
   private function assertResultErrors(ExecutionResult $result, array $expected): void {
-    // Retrieve the list of error strings.
-    $errors = array_map(function (Error $error) {
-      return $error->getMessage();
-    }, $result->errors);
-
     // Initalize the status.
     $unexpected = [];
-    $matchCount = array_map(function () {
-      return 0;
-    }, array_flip($expected));
+    $matchCount = array_fill_keys($expected, 0);
 
     // Iterate through error messages.
     // Collect unmatched errors and count pattern hits.
-    while ($error = array_pop($errors)) {
+    foreach ($result->errors as $error) {
+      $error_message = $error->getMessage();
       $match = FALSE;
       foreach ($expected as $pattern) {
-        if (@preg_match($pattern, $error) === FALSE) {
-          $match = $match || $pattern == $error;
+        if (@preg_match($pattern, $error_message) === FALSE) {
+          $match = $match || $pattern == $error_message;
           $matchCount[$pattern]++;
         }
         else {
-          $match = $match || preg_match($pattern, $error);
+          $match = $match || preg_match($pattern, $error_message);
           $matchCount[$pattern]++;
         }
       }
 
       if (!$match) {
-        $unexpected[] = $error;
+        $unexpected[] = $error_message;
       }
     }
 
@@ -181,8 +174,8 @@ private function assertResultErrors(ExecutionResult $result, array $expected): v
       return $count == 0;
     }));
 
-    $this->assertEquals([], $missing, "Missing errors:\n* " . implode("\n* ", $missing));
-    $this->assertEquals([], $unexpected, "Unexpected errors:\n* " . implode("\n* ", $unexpected));
+    self::assertEmpty($missing, "Missing errors:\n* " . implode("\n* ", $missing));
+    self::assertEmpty($unexpected, "Unexpected errors:\n* " . implode("\n* ", $unexpected));
   }
 
   /**