Book recommendations test suite

The test suite at scripts/test-book-recommendations.cjs catches bugs in the book recommendation pipeline before they reach production. Run it after any change to generate-book-recommendations.cjs or the library frontmatter parser.

node scripts/test-book-recommendations.cjs
# or
npm run test:books

What it tests

Frontmatter parser edge cases

• Empty quoted strings (author: "") must parse as '', not []
• Boolean values (true/false) parse as booleans
• Numeric strings stay as strings (no silent coercion)
• Arrays with items parse correctly
• Empty array literals ([]) parse as empty arrays

Output structure

• scored-books.json exists and is valid
• all_scored is an array with at least 10 books
• mix.main, mix.side, and mix.wildcard are all present

Type safety on every scored book

• title is a string
• author is a string
• scores is an object with a garden.score number

Content rules

• No books with status: read appear in the scored list

Lesson encoded

The frontmatter parser in generate-book-recommendations.cjs had a subtle bug: it stripped quotes before checking for an empty value. So author: "" became "" → strip quotes → "" (empty string) → value === '' check → assigned as [] (empty array). Arrays are truthy, so [] || "" returns [], and [].toLowerCase is not a function. The error was caught only at runtime in the browser, not during generation.

Fix: always check for empty before stripping quotes. If the raw value is "" or '', that is an explicit empty string, not an array start.

The corrected version in build-explore-data.cjs already had this right. The bug lived only in the copy made for the recommender script.