tasks/EA2_coverage_gap/spec.md

EA2: Coverage Gap — Add Tests to Reach 90% Branch Coverage

Goal

A Python data validation library has insufficient test coverage. Add tests to reach at least 90% branch coverage. The existing tests cover only the happy paths.

Coverage Measurement

pytest --cov=validator --cov-branch --cov-report=term-missing

Target: ≥ 90% branch coverage across all modules in validator/.

Library Structure

• validator/core.py — core validation functions: a domain-specific string validator (email/username/phone depending on seed), validate_range, validate_string
• validator/rules.py — rule classes: RequiredRule, TypeRule, PatternRule, RangeRule, ValidationError
• validator/pipeline.py — Pipeline class for chaining validation rules

What the Existing Tests Cover

tests/test_basic.py has 7 tests covering only success paths — valid inputs that pass validation. Coverage is approximately 40%. All the error/edge-case branches are uncovered.

Guidance on Where Gaps Typically Occur

Validation code commonly has uncovered branches in:

• Rejection paths: what happens when the input is invalid, malformed, empty, or None
• Boundary conditions: behavior when values exactly equal the minimum or maximum thresholds
• Configuration errors: what happens when the validator itself is misconfigured (e.g., min > max in a range)
• Pipeline behavior: what happens when there are no rules, when the first rule fails (early exit), when a duplicate rule is added, or when clear() is called on an empty pipeline
• Type coercion: behavior when values are of unexpected types

Use pytest --cov=validator --cov-branch --cov-report=term-missing to see exactly which lines and branches are uncovered.

Deliverables

• tests/test_validator.py with comprehensive tests targeting the uncovered branches
• Branch coverage ≥ 90% verified by pytest
• All existing tests still pass