test for date end being before date start

app/Plan/UseCases/CreatePlan.php

@@ -50,6 +50,13 @@ class CreatePlan
             throw new BadRequestException('date end is required');
         }
 
+        $startDate = new DateTimeImmutable($request->dateStart);
+        $endDate = new DateTimeImmutable($request->dateEnd);
+
+        if ($endDate < $startDate) {
+            throw new BadRequestException('date end cannot be before date start');
+        }
+
         $userId = $request->userId;
         $user = $this->userRepo->find($userId);
         if ($user === null) {