Function assert

example/tests/gm_xhr_test.js:1941–1943

(condition, msg)

  // ---------- Assertion utils ----------
  function assert(condition, msg) {
    if (!condition) throw new Error(msg || "assertion failed");
  }
  function assertEq(a, b, msg) {
    if (a !== b) throw new Error(msg ? `${msg}: expected ${b}, got ${a}` : `expected ${b}, got ${a}`);
  }