minor #38238 [Validator] stop using the deprecated at() PHPUnit matcher (xabbuh)

This PR was merged into the 5.1 branch.

Discussion
----------

[Validator] stop using the deprecated at() PHPUnit matcher

| Q             | A
| ------------- | ---
| Branch?       | 5.1
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
-------

0d0f92b7c6 stop using the deprecated at() PHPUnit matcher

Author: xabbuh

Test/ConstraintValidatorTestCase.php

@@ -24,6 +24,7 @@
 use Symfony\Component\Validator\ConstraintValidatorInterface;
 use Symfony\Component\Validator\ConstraintViolation;
 use Symfony\Component\Validator\ConstraintViolationInterface;
+use Symfony\Component\Validator\ConstraintViolationList;
 use Symfony\Component\Validator\Context\ExecutionContext;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
@@ -56,6 +57,8 @@ abstract class ConstraintValidatorTestCase extends TestCase
     protected $propertyPath;
     protected $constraint;
     protected $defaultTimezone;
+    private $expectedViolations;
+    private $call;
 
     protected function setUp(): void
     {
@@ -74,6 +77,9 @@ protected function setUp(): void
         $this->validator = $this->createValidator();
         $this->validator->initialize($this->context);
 
+        $this->expectedViolations = [];
+        $this->call = 0;
+
         \Locale::setDefault('en');
 
         $this->setDefaultTimezone('UTC');
@@ -107,6 +113,11 @@ protected function createContext()
         $translator = $this->getMockBuilder(TranslatorInterface::class)->getMock();
         $translator->expects($this->any())->method('trans')->willReturnArgument(0);
         $validator = $this->getMockBuilder('Symfony\Component\Validator\Validator\ValidatorInterface')->getMock();
+        $validator->expects($this->any())
+            ->method('validate')
+            ->willReturnCallback(function () {
+                return $this->expectedViolations[$this->call++] ?? new ConstraintViolationList();
+            });
 
         $context = new ExecutionContext($validator, $this->root, $translator);
         $context->setGroup($this->group);
@@ -260,11 +271,7 @@ protected function expectViolationsAt($i, $value, Constraint $constraint)
         $validator->initialize($context);
         $validator->validate($value, $constraint);
 
-        $this->context->getValidator()
-            ->expects($this->at($i))
-            ->method('validate')
-            ->willReturn($context->getViolations())
-        ;
+        $this->expectedViolations[] = $context->getViolations();
 
         return $context->getViolations();
     }