player command

app/src/main/java/chess/io/CommandExecutor.java

@@ -19,6 +19,10 @@ public class CommandExecutor {
 		assert this.outputSystem != null : "No output system specified !";
 
 		CommandResult result = command.execute(this.game, this.outputSystem);
+
+		// non player commands are not supposed to return move result
+		assert result != CommandResult.Moved || command instanceof PlayerCommand;
+
 		processResult(command, result);
 		return result;
 	}
@@ -34,7 +38,7 @@ public class CommandExecutor {
 
 			if (!needsPromote)
 				this.game.switchPlayerTurn();
-		} else if (command instanceof PromoteCommand) {
+		} else if (command instanceof PlayerCommand) {
 			this.game.switchPlayerTurn();
 		}
 	}