better createGame-Test

fh.fd.ci.server/src/main/java/de/fd/fh/server/game/GameService.java

@@ -15,6 +15,7 @@ public class GameService
 
     public GameId createGame(final UserId blackUser, final UserId whiteUser)
     {
-        return null;
+        final Game game = new Game(null, null, null, null, null, null);
+        return (GameId) repository.save(game).getId();
     }
 }

fh.fd.ci.server/src/test/java/de/fd/fh/server/game/GameServiceTest.java

@@ -7,8 +7,8 @@ import org.mockito.ArgumentCaptor;
 
 import static org.junit.jupiter.api.Assertions.*;
 import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.*;
 
 class GameServiceTest
 {
@@ -40,5 +40,14 @@ class GameServiceTest
         final ArgumentCaptor<Game> captor = ArgumentCaptor.forClass(Game.class);
 
         final GameId result = new GameService(repository).createGame(blackPlayer, whitePlayer);
+
+        verify(repository).save(captor.capture());
+
+        assertEquals("4242", result.getIdentifier());
+
+        assertNotNull(captor.getValue());
+
+        then(repository).should().save(any(Game.class));
+        then(repository).shouldHaveNoMoreInteractions();
     }
 }