fix: give the empty-field test case its own data provider

tests/Controller/Api/ApplicationFormControllerTest.php

@@ -274,13 +274,9 @@ class ApplicationFormControllerTest extends WebTestCase
      * An empty string is the shape a form posts for a field the visitor left blank, and it is as
      * unusable as an absent key - except for eu, where "" is a lawful no and has its own case.
      */
-    #[\PHPUnit\Framework\Attributes\DataProvider('requiredFields')]
+    #[\PHPUnit\Framework\Attributes\DataProvider('nonBlankFields')]
     public function testAPayloadWithAnEmptyRequiredFieldIsRejected(string $field): void
     {
-        if ('eu' === $field) {
-            $this->markTestSkipped('An empty eu is a no, not a missing answer - see its own test');
-        }
-
         $this->post([$field => ''] + $this->payload());
 
         $this->assertSame(Response::HTTP_BAD_REQUEST, $this->client->getResponse()->getStatusCode());
@@ -306,6 +302,21 @@ class ApplicationFormControllerTest extends WebTestCase
         yield 'city' => ['city'];
     }
 
+    /**
+     * The required fields that are NotBlank as well: all but eu, which is only NotNull because ""
+     * is a lawful no (testAnEmptyEuFlagIsNotAYes).
+     *
+     * @return iterable<string, array{string}>
+     */
+    public static function nonBlankFields(): iterable
+    {
+        foreach (self::requiredFields() as $name => $arguments) {
+            if ('eu' !== $name) {
+                yield $name => $arguments;
+            }
+        }
+    }
+
     /**
      * The one field whose format is nailed down: provisioning parses it as a date, so the day the
      * TYPO3 side switches a form back to a free-text birthday has to be a 400 here rather than a