If your Yii2 app is set up with Codeception and its [Yii2][1] module for automated tests, the regular log output of the app will show in the terminal when increasing the verbosity of codecept (at least two levels: -vv).
For example, if in a backend controller action MoveAction.php I add
Yii::error("I am an error");
Yii::warning("I am a warning");
Yii::info("I am an info");
Yii::debug("I am a debug");
Yii::trace("I am a trace");