Small unit tests give fast feedback

A one thousand rupiah discount error can silently corrupt every checkout receipt for a whole day.

I test the smallest unit in isolation so logic mistakes surface within seconds, not days.

Atlassian describes unit tests as the fast foundation teams rerun every single day.

I use mocks for APIs and databases so tests stay deterministic without depending on the network.

Frequent small tests build courage to refactor because every regression shows up immediately.

If E2E tests stay small and rare shapes the suite, then CI gates every change early turns speed into habit.

I keep unit tests largest whenever fast cheap signal matters more than realism.