Philip Garrett > Test-Spec-0.46 > Test::Spec::Mocks

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NAME ^

Test::Spec::Mocks - Object Simulation Plugin for Test::Spec

SYNOPSIS ^

  use Test::Spec;
  use base qw(Test::Spec);

  use My::RSS::Tool;    # this is what we're testing
  use LWP::UserAgent;

  describe "RSS tool" => sub {
    it "should fetch and parse an RSS feed" => sub {
      my $xml = load_rss_fixture();
      LWP::Simple->expects('get')->returns($xml);

      # calls LWP::Simple::get, but returns our $xml instead
      my @stories = My::RSS::Tool->run;

      is_deeply(\@stories, load_stories_fixture());
    };
  };

DESCRIPTION ^

Test::Spec::Mocks is a plugin for Test::Spec that provides mocking and stubbing of objects, individual methods and plain subroutines on both object instances and classes. This module is inspired by and heavily borrows from Mocha, a library for the Ruby programming language. Mocha itself is inspired by JMock.

Mock objects provide a way to simulate the behavior of real objects, while providing consistent, repeatable results. This is very useful when you need to test a function whose results are dependent upon an external factor that is normally uncontrollable (like the time of day). Mocks also allow you to test your code in isolation, a tenet of unit testing.

There are many other reasons why mock objects might come in handy. See the Mock objects article at Wikipedia for lots more examples and more in-depth coverage of the philosophy behind object mocking.

Ecosystem

Test::Spec::Mocks is currently only usable from within tests built with the Test::Spec BDD framework.

Terminology

Familiarize yourself with these terms:

Using stub objects (anonymous stubs)

Sometimes the code you're testing requires that you pass it an object that conforms to a specific interface. For example, you are testing a console prompting library, but you don't want to require a real person to stand by, waiting to type answers into the console. The library requires an object that returns a string when the read_line method is called.

You could create a class specifically for returning test console input. But why do that? You can create a stub object in one line:

  describe "An Asker" => sub {
    my $asker = Asker->new;

    it "returns true when a yes_or_no question is answered 'yes'" => sub {
      my $console_stub = stub(read_line => "yes");
      # $console_stub->read_line returns "yes"
      ok( $asker->yes_or_no($console_stub, "Am I awesome?") );
    };

    it "returns false when a yes_or_no question is answered 'no'" => sub {
      my $console_stub = stub(read_line => "no");
      ok( ! $asker->yes_or_no($console_stub, "Am I second best?") );
    };
  };

Stubs can also take subroutine references. This is useful when the behavior you need to mimic is a little more complex.

  it "keeps asking until it gets an answer" => sub {
    my @answers = (undef, "yes");
    my $console_stub = stub(read_line => sub { shift @answers });
    # when console_stub is called the first time, it returns undef
    # the second time returns "yes"
    ok( $asker->yes_or_no($console_stub, "Do I smell nice?") );
  };

Using mock objects

If you want to take your tests one step further, you can use mock objects instead of stub objects. Mocks ensure the methods you expect to be called actually are called. If they aren't, the mock will raise an exception which causes your test to fail.

In this example, we are testing that read_line is called once and only once (the default for mocks).

  it "returns true when a yes_or_no question is answered 'yes'" => sub {
    my $console_mock = mock()->expects('read_line')->returns("yes");
    # $console_mock->read_line returns "yes"
    ok( $asker->yes_or_no($console_mock, "Am I awesome?") );
  };

If Asker's yes_or_no method doesn't call read_line on our mock exactly one time, the test would fail with a message like:

  expected read_line to be called exactly 1 time, but it was called 0 times

You can specify how many times your mock should be called with "exactly":

  it "keeps asking until it gets an answer" => sub {
    my @answers = (undef, "yes");
    my $console_mock = mock();
    $console_mock->expects('read_line')
                 ->returns(sub { shift @answers })
                 ->exactly(2);
    # when console_mock is called the first time, it returns undef
    # the second time returns "yes"
    ok( $asker->yes_or_no($console_mock, "Do I smell nice?") );
  };

If you want something more flexible than "exactly", you can choose from "at_least", "at_most", "any_number" and others. See "EXPECTATION ADJUSTMENT METHODS".

Stubbing methods

Sometimes you want to override just a small subset of an object's behavior.

  describe "The old audit system" => sub {
    my $dbh;
    before sub { $dbh = SomeExternalClass->get_dbh };

    it "executes the expected sql" => sub {
      my $sql;
      $dbh->stubs(do => sub { $sql = shift; return 1 });

      # $dbh->do("foo") now sets $sql to "foo"
      # $dbh->quote still does what it normally would

      audit_event($dbh, "server crash, oh noes!!");

      like( $sql, qr/insert into audit_event.*'server crash, oh noes!!!'/ );
    };
  };

You can also stub class methods:

  # 1977-05-26T14:11:55
  my $event_datetime = DateTime->new(from_epoch => 0xdeafcab);

  it "should tag each audit event with the current time" => sub {
    DateTime->stubs('now' => sub { $event_datetime });
    is( audit_timestamp(), '19770526.141155' );
  };

Mocking methods

Mocked methods are to stubbed methods as mock objects are to stub objects.

  it "executes the expected sql" => sub {
    $dbh->expects('do')->returns(sub { $sql = shift; return 1 });

    # $dbh->do("foo") now sets $sql to "foo"
    # $dbh->quote still does what it normally would

    audit_event($dbh, "server crash, oh noes!!");
    like( $sql, qr/insert into audit_event.*'server crash, oh noes!!!'/ );

    # if audit_event doesn't call $dbh->do exactly once, KABOOM!
  };

CONSTRUCTORS ^

stub()
stub($method_name => $result, ...)
stub($method_name => sub { $result }, ...)
stub({ $method_name => $result, ... })

Returns a new anonymous stub object. Takes a list of $method_name/$result pairs or a reference to a hash containing the same. Each $method_name listed is stubbed to return the associated value ($result); or if the value is a subroutine reference, it is stubbed in-place (the subroutine becomes the method).

Examples:

  # A blank object with no methods.
  # Gives a true response to ref() and blessed().
  my $blank = stub();

  # Static responses to width() and height():
  my $rect = stub(width => 5, height => 5);

  # Dynamic response to area():
  my $radius = 1.0;
  my $circle_stub = stub(area => sub { PI * $radius * $radius });

You can also stub more methods, just like with any other object:

  my $rect = stub(width => 5, height => 5);
  $rect->stubs(area => sub { my $self = shift; $self->width * $self->height });
$thing->stubs($method_name)
$thing->stubs($method_name => $result)
$thing->stubs($method_name => sub { $result })
$thing->stubs({ $method_name => $result })

Stubs one or more methods on an existing class or instance, $thing.

If passed only one (non-hash) argument, it is interpreted as a method name. The return value of the stubbed method will be undef.

Otherwise, the arguments are a list of $method_name and $result pairs, either as a flat list or as a hash reference. Each method is installed onto $thing, and returns the specified result. If the result is a subroutine reference, it will be called for every invocation of the method.

mock()

Returns a new blank, anonymous mock object, suitable for mocking methods with expects().

  my $rect = mock();
  $rect->expects('area')->returns(100);
$thing->expects($method)

Installs a mock method named $method onto the class or object $thing and returns an Test::Spec::Mocks::Expectation object, which you can use to set the return value with returns() and other expectations. By default, the method is expected to be called at_least_once.

If the expectation is not met before the enclosing example completes, the mocked method will raise an exception that looks something like:

  expected foo to be called exactly 1 time, but it was called 0 times

EXPECTATION ADJUSTMENT METHODS ^

These are methods of the Test::Spec::Mocks::Expectation class, which you'll receive by calling expects() on a class or object instance.

returns( $result )
returns( @result )
returns( \&callback )

Configures the mocked method to return the specified result when called. If passed a subroutine reference, the subroutine will be executed when the method is called, and the result is the return value.

  $rect->expects('height')->returns(5);
  # $rect->height ==> 5

  @points = ( [0,0], [1,0], [1,1], [1,0] );
  $rect->expects('points')->returns(@points);
  # (@p = $rect->points) ==> ( [0,0], [1,0], [1,1], [1,0] )
  # ($p = $rect->points) ==> 4

  @points = ( [0,0], [1,0], [1,1], [1,0] );
  $rect->expects('next_point')->returns(sub { shift @points });
  # $rect->next_point ==> [0,0]
  # $rect->next_point ==> [1,0]
  # ...
exactly($N)

Configures the mocked method so that it must be called exactly $N times.

never

Configures the mocked method so that it must never be called.

once

Configures the mocked method so that it must be called exactly one time.

at_least($N)

Configures the mocked method so that it must be called at least $N times.

at_least_once

Configures the mocked method so that it must be called at least 1 time. This is just syntactic sugar for at_least(1).

at_most($N)

Configures the mocked method so that it must be called no more than $N times.

at_most_once

Configures the mocked method so that it must be called either zero or 1 times.

maybe

An alias for "at_most_once".

any_number

Configures the mocked method so that it can be called any number of times.

times

A syntactic sugar no-op:

  $io->expects('print')->exactly(3)->times;

This method is alpha and will probably change in a future release.

with(@arguments)

Configures the mocked method so that it must be called with arguments as specified. The arguments will be compared using the "eq" operator, so it works for most scalar values with no problem. If you want to check objects here, they must be the exact same instance or you must overload the "eq" operator to provide the behavior you desire.

raises($exception)

Configures the mocked method so that it raises $exception when called.

OTHER EXPECTATION METHODS ^

verify

Allows you to verify manually that the expectation was met. If the expectation has not been met, the method dies with an error message containing specifics of the failure. Returns true otherwise.

problems

If the expectation has not been met, returns a list of problem description strings. Otherwise, returns an empty list.

SEE ALSO ^

There are other less sugary mocking systems for Perl, including Test::MockObject and Test::MockObject::Extends.

This module is a plugin for Test::Spec. It is inspired by Mocha.

The Wikipedia article Mock object is very informative.

AUTHOR ^

Philip Garrett, <philip.garrett@icainformatics.com>

COPYRIGHT & LICENSE ^

Copyright (c) 2011 by Informatics Corporation of America.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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