Write unit tests for a function

import { describe, it, expect } from "vitest";
import { parseDuration } from "./parseDuration";

describe("parseDuration", () => {
  it("parses combined hours and minutes like '1h30m' as 5400 seconds", () => {
    expect(parseDuration("1h30m")).toBe(5400);
  });

  it("parses single-unit inputs like '45s' and '2m' correctly", () => {
    expect(parseDuration("45s")).toBe(45);
    expect(parseDuration("2m")).toBe(120);
  });

  it("returns 0 for an empty string", () => {
    expect(parseDuration("")).toBe(0);
  });

  it("throws on non-duration text like 'abc' instead of returning 0", () => {
    expect(() => parseDuration("abc")).toThrow();
  });

  it("throws when a trailing number has no unit, like '1h30'", () => {
    expect(() => parseDuration("1h30")).toThrow();
  });

  it("throws when units are out of order, like '30m1h'", () => {
    expect(() => parseDuration("30m1h")).toThrow();
  });

  it("throws on negative values like '-5s'", () => {
    expect(() => parseDuration("-5s")).toThrow();
  });

  it("throws on decimal values like '1.5h'", () => {
    expect(() => parseDuration("1.5h")).toThrow();
  });
});

Bugs the tests reveal

1. Regex is not anchored. match() finds a substring anywhere in the input, so almost any string matches. "abc" returns 0 silently.
2. Invalid input silently returns 0. Because every group is optional, the regex matches the empty string on any input, so errors are never surfaced.
3. Trailing numbers without units are ignored. "1h30" returns 3600, dropping the 30.
4. Unit order is not enforced. "30m1h" returns 1800, dropping the 1h.
5. Negative values are unsupported. "-5s" returns 0 instead of an error.
6. Decimal values are unsupported. "1.5h" returns 0. The .5 is discarded and the h is never matched, so the result is wrong without any error.