Test coverage for packages/billing is 71%. The biggest gaps:

1. proration.ts at 38%: no tests for mid-cycle downgrades.
2. tax.ts at 52%: EU reverse-charge path is untested.
3. invoice-pdf.ts at 60%: rendering failures are not covered.

I wrote 9 tests for the proration gaps; coverage there is now 84%.

The 9 tests cover:

• Mid-cycle downgrade with credit carryover
• Downgrade on the last day of the cycle
• Same-day upgrade then downgrade
• Leap-year February cycles
• Zero-amount plans
• Four currency rounding cases

Reverse-charge needs three cases: valid VAT id, invalid VAT id, and a non-EU buyer. I wrote them and coverage for tax.ts rose from 52% to 79%.

Package coverage is now 77%. Remaining gap is invoice-pdf.ts at 60%, which needs a fixture for the failure path.