A mistake less experienced software engineers make when it comes to estimations:

They break out maintainability/quality. Eg “building the feature is 2 weeks, adding automated tests another 3 days”.

What follows by less technical stakeholders is a push to remove the latter.

Non-functional requirements like correctness, quality, maintainability, performance etc should be baked into estimates, and not made part of bargaining. That bargaining is how sw can become less maintainable over time.