Add Focused Financial Tests

Add the root test script first, then open tests/finance.test.js and test the functions most likely to regress.

In the root package.json, add:

{
  "type": "module",
  "scripts": {
    "test": "node --test"
  }
}

Keep the existing scripts; merge these fields into the current package file rather than replacing it.

Good targets include:

isValidDateOnly("2026-02-29");
parseAmountToCents("84.50");
calculateAverageMonthlyExpenseCents(months);
calculateTotals(transactions);
computeCategoryTotals(transactions, categories);
validateTransactionInput(body, categories);

Keep these tests dependency-free with Node’s built-in test runner and assertions.

Test it

Run:

npm test

Checkpoint

The financial rules can be checked without opening a browser.