chore: verify the ISO-2 country move and renumber its migration

migrations/Version20260927090000.php

@@ -16,7 +16,7 @@ use Doctrine\Migrations\AbstractMigration;
  * existing rows are converted to match. The flag icons and the country filters use the
  * same vocabulary and are switched with it.
  */
-final class Version20260813120000 extends AbstractMigration
+final class Version20260927090000 extends AbstractMigration
 {
     private const TO_ISO = [
         'a' => 'at',

tests/Service/Common/AbstractFilterHandlerTest.php

@@ -0,0 +1,88 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Service\Common;
+
+use App\Model\AbstractFilterDto;
+use App\Model\AssignmentFilterDto;
+use App\Service\Common\AbstractFilterHandler;
+use Doctrine\ORM\EntityManagerInterface;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpFoundation\RequestStack;
+
+/**
+ * destination.country moved from the lowercased BusProNet abbreviations to ISO-2, but a
+ * session written before the deploy still holds the old value, and the filter is restored
+ * from the session rather than from the form. Without the translation those users would
+ * filter for a value no destination carries any more and see an empty list.
+ *
+ * Only a, ch, f and i can ever be in a session: those were the only four the filter forms
+ * offered. All four land inside the new choice list, so no stale value can fall outside it.
+ */
+class AbstractFilterHandlerTest extends TestCase
+{
+    /**
+     * @dataProvider legacyCountries
+     */
+    public function testALegacyCountryIsTranslatedToItsIsoCode(?string $stored, ?string $expected): void
+    {
+        $this->assertSame($expected, $this->handler()->translate($stored));
+    }
+
+    /**
+     * @return iterable<string, array{0: ?string, 1: ?string}>
+     */
+    public static function legacyCountries(): iterable
+    {
+        // the four the filter forms offered, which is all a session can hold
+        yield 'Österreich' => ['a', 'at'];
+        yield 'Frankreich' => ['f', 'fr'];
+        yield 'Italien' => ['i', 'it'];
+        yield 'Schweiz was already ISO' => ['ch', 'ch'];
+
+        // never offered by a filter, so unreachable from a session - translated anyway
+        yield 'Deutschland' => ['d', 'de'];
+        yield 'Niederlande was already ISO' => ['nl', 'nl'];
+
+        yield 'no filter set' => [null, null];
+        yield 'an already migrated value is left alone' => ['at', 'at'];
+        yield 'an unknown value is not invented away' => ['xx', 'xx'];
+    }
+
+    public function testEveryTranslatedValueIsOfferedByTheFilterForm(): void
+    {
+        // what AssignmentFilterType and ApplicationFilterType offer
+        $offered = ['at', 'ch', 'fr', 'it'];
+        $handler = $this->handler();
+
+        foreach (['a', 'ch', 'f', 'i'] as $storable) {
+            $this->assertContains(
+                $handler->translate($storable),
+                $offered,
+                sprintf('A session holding "%s" would filter for a value the form cannot show', $storable),
+            );
+        }
+    }
+
+    private function handler(): object
+    {
+        return new class($this->createMock(RequestStack::class), $this->createMock(EntityManagerInterface::class)) extends AbstractFilterHandler {
+            protected string $modelClass = AssignmentFilterDto::class;
+
+            public function translate(?string $country): ?string
+            {
+                return $this->toIsoCountry($country);
+            }
+
+            public function getFilterSettings(): AbstractFilterDto
+            {
+                return new AssignmentFilterDto();
+            }
+
+            protected function saveFilterSettings(AbstractFilterDto $filterDto): void
+            {
+            }
+        };
+    }
+}