matchAsync method

  1. @override
dynamic matchAsync(
  1. Object? item

Returns null if this matches item, or a String description of the failure if it doesn't match.

This can return a Future or a synchronous value. If it returns a Future, neither expect nor the test will complete until that Future completes.

If this returns a String synchronously, expect will synchronously throw a TestFailure and matches will synchronously return false.


dynamic /*FutureOr<String>*/ matchAsync(Object? item) {
  if (item is! Function && item is! Future) {
    return 'was not a Function or Future';

  if (item is Future) {
    return _matchFuture(item, 'emitted ');

  try {
    item as Function;
    var value = item();
    if (value is Future) {
      return _matchFuture(value, 'returned a Future that emitted ');

    return indent(prettyPrint(value), first: 'returned ');
  } catch (error, trace) {
    return _check(error, trace);