Function assertThrows

assert/throws.ts:59–111

(
  fn: () => unknown,
  errorClassOrMsg?:
    // deno-lint-ignore no-explicit-any
    | (abstract new (...args: any[]) => E)
    | string,
  msgIncludesOrMsg?: string,
  msg?: string,
)

  msg?: string,
): E;
export function assertThrows<E extends Error = Error>(
  fn: () => unknown,
  errorClassOrMsg?:
    // deno-lint-ignore no-explicit-any
    | (abstract new (...args: any[]) => E)
    | string,
  msgIncludesOrMsg?: string,
  msg?: string,
): E | Error | unknown {
  // deno-lint-ignore no-explicit-any
  let ErrorClass: (abstract new (...args: any[]) => E) | undefined;
  let msgIncludes: string | undefined;
  let err;

  if (typeof errorClassOrMsg !== "string") {
    if (
      errorClassOrMsg === undefined ||
      errorClassOrMsg?.prototype instanceof Error ||
      errorClassOrMsg?.prototype === Error.prototype
    ) {
      ErrorClass = errorClassOrMsg;
      msgIncludes = msgIncludesOrMsg;
    } else {
      msg = msgIncludesOrMsg;
    }
  } else {
    msg = errorClassOrMsg;
  }
  let doesThrow = false;
  const msgSuffix = msg ? `: ${msg}` : ".";
  try {
    fn();
  } catch (error) {
    if (ErrorClass) {
      if (error instanceof Error === false) {
        throw new AssertionError(`A non-Error object was thrown${msgSuffix}`);
      }
      assertIsError(
        error,
        ErrorClass,
        msgIncludes,
        msg,
      );
    }
    err = error;
    doesThrow = true;
  }
  if (!doesThrow) {
    msg = `Expected function to throw${msgSuffix}`;
    throw new AssertionError(msg);
  }
  return err;
}