Test data builders and fixtures

Builders and factories express only the fields relevant to each test—`UserBuilder().withRole('admin').build()`—avoiding 50-line object literals. Fixtures load shared baseline data; prefer function-scoped setup over global beforeAll that couples unrelated tests.

Factories should default valid data and allow overrides; keep randomness explicit and seeded.

On interviews: show how a builder reduced duplication without hiding the behavior under test.

Common pitfalls: mega-fixtures every test mutates, builders with hidden side effects (auto-insert DB), and copy-paste literals diverging from production schema.

The trade-off is readability versus indirection—builders help until you need to read three files to understand one test.

Checklist:

• Defaults valid; override only differing fields.
• Scope fixtures to describe blocks or tests.
• Align factory shapes with API/schema types.