tests(UserApiController): Mock getDisplayName return value

Signed-off-by: Julius Härtl <jus@bitgrid.net>

Author: juliusknorr

tests/unit/Controller/UserApiControllerTest.php

@@ -69,6 +69,9 @@ public function testUsersIndex(int $documentId, int $sessionId, string $sessionT
 				'userId' => 'admin',
 				'displayName' => 'admin',
 			]]);
+		$this->userManager->expects($this->once())
+			->method('getDisplayName')
+			->willReturn('Administrator');
 		$this->sessionService
 			->expects($this->once())
 			->method('getSession')->willReturn($session);