import static org.assertj.core.api.Assertions.assertThat;

public class LerneJoining {
    public static void main(String[] args) {
        List<String> bros = TestDataProvider.getBrothersInArms();
        String brosString = bros.stream().collect(Collectors.joining(", ")); //Collectors.joining(...)
        assertThat(brosString).isEqualTo("Walther, Hans, Erich, Paul");
    }
}