fix data provider which randomly generate invalid data in test

src/Bundle/ChillPersonBundle/Tests/Controller/AccompanyingCourseApiControllerTest.php

@@ -553,11 +553,24 @@ class AccompanyingCourseApiControllerTest extends WebTestCase
         $center = $em->getRepository(Center::class)
             ->findOneBy(array('name' => 'Center A'));
 
-        $personIds = $em->createQuery("SELECT p.id FROM ".
-            Person::class." p ".
-            " WHERE p.center = :center")
+        $qb = $em->createQueryBuilder();
+        $personIds = $qb
+            ->select('p.id')
+            ->from(Person::class, 'p')
+            ->where(
+                $qb->expr()->eq(
+                    'p.center',
+                    ':center'
+                )
+            )
+            ->andWhere(
+                $qb->expr()->gt(
+                    'SIZE(p.accompanyingPeriodParticipations)',
+                    0)
+                )
             ->setParameter('center', $center)
             ->setMaxResults($maxResults)
+            ->getQuery()
             ->getScalarResult();
 
         // create a random order