IO::Async::Test - utility functions for use in test scripts


   use Test::More tests => 1;
   use IO::Async::Test;

   use IO::Async::Loop;
   my $loop = IO::Async::Loop->new;
   testing_loop( $loop );

   my $result;

      some => args,

      on_done => sub {
         $result = the_outcome;

   wait_for { defined $result };

   is( $result, what_we_expected, 'The event happened' );


   my $buffer = "";
   my $handle = IO::Handle-> ...

   wait_for_stream { length $buffer >= 10 } $handle => $buffer;

   is( substr( $buffer, 0, 10, "" ), "0123456789", 'Buffer was correct' );

   my $result = wait_for_future( $stream->read_until( "\n" ) )->get;


This module provides utility functions that may be useful when writing test scripts for code which uses IO::Async (as well as being used in the IO::Async test scripts themselves).

Test scripts are often synchronous by nature; they are a linear sequence of actions to perform, interspersed with assertions which check for given conditions. This goes against the very nature of IO::Async which, being an asynchronisation framework, does not provide a linear stepped way of working.

In order to write a test, the wait_for function provides a way of synchronising the code, so that a given condition is known to hold, which would typically signify that some event has occurred, the outcome of which can now be tested using the usual testing primitives.

Because the primary purpose of IO::Async is to provide IO operations on filehandles, a great many tests will likely be based around connected pipes or socket handles. The wait_for_stream function provides a convenient way to wait for some content to be written through such a connected stream.



   testing_loop( $loop )

Set the IO::Async::Loop object which the wait_for function will loop on.


   wait_for { COND } OPTS

Repeatedly call the loop_once method on the underlying loop (given to the testing_loop function), until the given condition function callback returns true.

To guard against stalled scripts, if the loop indicates a timeout for (a default of) 10 consequentive seconds, then an error is thrown.

Takes the following named options:

timeout => NUM

The time in seconds to wait before giving up the test as being stalled. Defaults to 10 seconds.


   wait_for_stream { COND } $handle, $buffer

As wait_for, but will also watch the given IO handle for readability, and whenever it is readable will read bytes in from it into the given buffer. The buffer is NOT initialised when the function is entered, in case data remains from a previous call.

$buffer can also be a CODE reference, in which case it will be invoked being passed data read from the handle, whenever it is readable.


   $future = wait_for_future $future

Since version 0.68.

A handy wrapper around using wait_for to wait for a Future to become ready. The future instance itself is returned, allowing neater code.


Paul Evans <>