Leverkusen will face Lens and Arsenal in the next two friendlies. And these two teams are strong enough. Xabi will get an idea of what his squad is capable of in the match against Lens. And I'm looking forward to Arsenal vs Leverkusen. In this match we will get an idea about the strength of both the teams.
Leverkusen will face a much more interesting match because facing Arsenal will provide a real picture of the strength of Xabi Alonso's team next season. Likewise with Arsenal where Areta can make team adjustments before facing the official competition.
I agree with you. The quality of new players in the squad can be tested during the pre-season matches. New players who are added to the squad can be checked if they are fit for the squad. Also, coaches can experiment with different match strategies in pre-season matches. If the coach can successfully experiment and identify the weaknesses of the team, then it is possible to maintain the stability of the performance from the beginning of the season. But if the internal problems or weaknesses in the squad are not identified, the team's performance at the start of the season will be slow and erratic.
Leverkusen were last season's champions. The Bundesliga title will definitely be their target next season. And since Bayern Munich will be doing their best to regain their old dominance next season, it will be much more difficult for Leverkusen to become Bundesliga champions. So Xabi Alonso will try to stabilize the team before the start of the season.