Test::Ratchet - Mocking helper that swaps out implementations automatically


version 0.005


    use Test::Ratchet qw(ratchet clank);
    use Test::MockModule;
    use Test::More;

    use Some::Module;

    my $mock = Test::MockModule->new('Some::Module');
    $mock->mock( magic_method => ratchet(

        # A clank *must* be run, or the test fails!
        clank \&third_implementation,

    # In reality, you will have no control over the use of this object - which
    # is the purpose of the module in the first place! The actual use of this
    # object would be deep in the code you are actually testing.
    my $obj = Some::Module->new;

    $obj->magic_method('foo'); # Returns { something => 'relevant' }
    $obj->magic_method('bar'); # Returns { something => 'else' }

    # This test will fail! magic_method was only run twice, but there are three
    # implementations - and the third one is a clank! Failing to run a clank
    # causes a test failure.

    sub first_implementation {
        my $self = shift;
        my $arg1 = shift;

        is $arg1, "foo", "First call passed foo to magic_method";

        return { something => 'relevant' }

    sub second_implementation {
        my $self = shift;
        my $arg1 = shift;

        is $arg1, "bar", "Second call passed bar to magic_method";

        return { something => 'else' }

    sub third_implementation {
        my $self = shift;
        my $arg1 = shift;

        is $arg1, "zip", "Third call passed zip to magic_method";

        return { something => 'different' }


Testing sucks, especially when you have to deal with third-party code, especially when you didn't have a choice about which third-party code you are relying on.

This module solves one specific difficulty of doing so: when you have an atomic operation that ends up running the same function multiple times with different data.

An example you say? The rationale for writing this module was to test a module that used "PATCH" in REST::Client twice in the same function, but sending different data to different endpoints (because Reasons). Since the function being tested could not be subdivided by the test, it made sense to set up a sequence of expectations before the test instead.

This module, then, simply exports the "ratchet" function, which sets up a queue of subrefs to handle a mocked function.

I'm sure it has other purposes too.


This module exports "ratchet" and "clank" on request.


Accepts any number of subrefs, and returns a single subref that will run through this queue each time it is called.

Additionally, non-refs can be used to repeat an entry rather than creating multiple refs to the same thing:


A number will repeat the subref after it N times


An asterisk will repeat the subref after it indefinitely.

If the mocked sub is called and the queue has expired, it will die.


A clank is a subref that outputs a test failure if it is not run at least once before it goes out of scope. You can use it in your ratchet, or independently.

    ratchet (
        clank \&must_run,

To keep the interface simple the test failure uses a generic message that tells you as best as it can the script and line number at which the clank appears.

I recommend that you ensure your clank goes out of scope before you end your test suite, so that you don't accidentally output your test summary before it has a chance to fail.

        my $mock = Test::MockModule->new(...);
        $mock->mock('method', clank sub { ... });
        ... tests ...



Alastair Douglas <>


This software is Copyright (c) 2020 by Alastair Douglas.

This is free software, licensed under:

  The MIT (X11) License