Function assertRejects

assert/rejects.ts:56–123

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

  msg?: string,
): Promise<E>;
export async function assertRejects<E extends Error = Error>(
  fn: () => PromiseLike<unknown>,
  errorClassOrMsg?:
    // deno-lint-ignore no-explicit-any
    | (abstract new (...args: any[]) => E)
    | string,
  msgIncludesOrMsg?: string,
  msg?: string,
): Promise<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 = errorClassOrMsg;
  }
  let doesThrow = false;
  let isPromiseReturned = false;
  const msgSuffix = msg ? `: ${msg}` : ".";
  try {
    const possiblePromise = fn();
    if (
      possiblePromise &&
      typeof possiblePromise === "object" &&
      typeof possiblePromise.then === "function"
    ) {
      isPromiseReturned = true;
      await possiblePromise;
    } else {
      throw new Error();
    }
  } catch (error) {
    if (!isPromiseReturned) {
      throw new AssertionError(
        `Function throws when expected to reject${msgSuffix}`,
      );
    }
    if (ErrorClass) {
      if (!(error instanceof Error)) {
        throw new AssertionError(`A non-Error object was rejected${msgSuffix}`);
      }
      assertIsError(
        error,
        ErrorClass,
        msgIncludes,
        msg,
      );
    }