var funcs []func() error
	for _, backend := range u.backends {
		backend := backend
		funcs = append(funcs, func() error {
			return backend.Run(stopCh)
		})
	}
	return errors.AggregateGoroutines(funcs...)
}

func (u union) Shutdown() {
	for _, backend := range u.backends {
		backend.Shutdown()
	}
}

func (u union) String() string {
	var backendStrings []string

		case 1:
			return agg.Errors()[0]
		case 0:
			return nil
		}
	}
	return err
}

// AggregateGoroutines runs the provided functions in parallel, stuffing all
// non-nil errors into the returned Aggregate.
// Returns nil if all the functions complete successfully.
func AggregateGoroutines(funcs ...func() error) Aggregate {
	errChan := make(chan error, len(funcs))
	for _, f := range funcs {

	for i, testCase := range testCases {
		funcs := make([]func() error, len(testCase.errs))
		for i := range testCase.errs {
			err := testCase.errs[i]
			funcs[i] = func() error { return err }
		}
		agg := AggregateGoroutines(funcs...)
		if agg == nil {
			if len(testCase.expected) > 0 {
				t.Errorf("%d: expected %v, got nil", i, testCase.expected)
			}
			continue
		}
		if len(agg.Errors()) != len(testCase.expected) {