fix test not properly setting non exististing user

Signed-off-by: Marvin Winkens <[email protected]>

tests/Command/AnnounceTest.php

@@ -178,7 +178,7 @@ public function testExecuteException($user, $subject, $message, $group, $activit
 		$this->setupInput($user, $subject, $message, $group, $activites, $notifications, $emails, $comments, $scheduleTime, $deleteTime);
 		$this->userManager->expects($this->once())
 			->method('userExists')
-			->willReturn(true);
+			->willReturn($user !== 'invalid');
 		$this->time->expects($this->any())
 			->method('getTime')
 			->willReturn(10);