fix: resolve failing tests across utility library

[stooit]

Summary

Fixes all 16 previously-failing tests across the utility library. The suite now reports 60 pass / 0 fail, with npx tsc --noEmit clean. No test files were modified and no dependencies were added.

Changes by file

• src/calculator.ts — divide throws Error("Division by zero") when the divisor is 0 instead of silently returning Infinity.
• src/string-utils.ts
  • wordCount — trims then splits on /\s+/ so runs of whitespace no longer inflate the count ("hello world" → 2). Also handles tabs/newlines.
  • truncate — implemented: returns the string unchanged when str.length <= maxLength; otherwise truncates at a word boundary, reserving 3 chars for "..." so the ellipsis counts toward maxLength. Falls back to a hard slice when maxLength <= 3 so the result never exceeds maxLength.
• src/date-utils.ts — diffDays uses Math.round(Math.abs(hours)/24) to fix the off-by-one (36h now → "2 days ago"), and corrects a latent bug on the future-date branch.
• src/task-manager.ts — implemented/completed remove (returns whether a task existed), update (applies only supplied keys, returns false for a missing id), and sortBy (priority, status, and createdAt ordering).
• src/validator.ts
  • isEmail — supports multi-level subdomains and longer TLDs, and rejects empty/consecutive-dot labels.
  • isUrl — accepts URLs with explicit ports (e.g. http://localhost:3000) while still allowlisting http/https.

Testing

• bun test → 60 pass, 0 fail
• npx tsc --noEmit → exit 0

Assumptions

• The tests are the authoritative spec; changes were kept minimal to satisfy them without altering unrelated behaviour.
• truncate guarantees its return value never exceeds maxLength, hard-slicing when there is no room for a word plus ellipsis.
• update treats an omitted field as "leave unchanged" and only allows explicitly clearing the optional description.

Note

isEmail is a syntactic check only — if used to gate account creation, pair it with a confirmation-link verification step.