Extract a Pricing Rule Without Moving the Bug
Execute Extract Function as a sequence of behavior-preserving steps.
Fix the premium-plan discount rule hidden inside a long invoice builder without making the bug fix harder to review. Extract Function: name the policy, preserve behavior, then change the policy. Changing the discount conditional in place mixes policy change with navigation through logging, formatting, and subtotal code. If the test fails, nobody knows whether the extraction or the rule caused it. Find the coherent idea Select only the lines that decide the premium discount rate. The slice has one job and a name the caller can read. Extract without editing logic Move those lines to premiumDiscountRate(customer, invoice) and pass the…
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