Steven Lembark > Object-Exercise > Object::Exercise



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Object::Exercise - Generic execution & benchmark harness for method calls.


    use Object::Exercise;

    # at this point $exercise is defined as a 
    # coderef to execute the tests.

    my @test_opz =
            # no arrayref: call $obj->$method( @argz )
            # check for $@ with message of method and args.

            qw( method arg arg arg )

            # two arrayrefs:
            # [ method and args ], 
            # [ compare values ]

            [ method arg arg arg ... ]
            [ 1 ],

            # if a method is expected to fail, store
            # a literal 'undef' as the second element.
            [ qw( method expected to fail ) ]

            # use a pre-defined message rather than
            # join the method and args.

            [ method => @argz ],
            [ ( 1 .. 10 )     ],
            'Coderef returns list'

            # use a coderef to dispatch the call rather
            # than a method name.
            # storing a literal undef as an array value
            # checks for an undef -- vs. ignoring the 
            # return value in the example above.

            [ $subref, @argz ],
            [ undef ],
            'Coderef returns list'

            # compare the method return via regex
            # effectively:
            # $obj->Foobar( @argz ) =~ qr/Foo.*Bar/

            [ method => @argz ],
            'method returns text of Foo ... Bar'

            # compare the return via user-supplied 
            # filter (instead of cmp_deeply).

            [ method => @argz ],

        # turn on verbosity


        # subref is called to validate the result when static
        # values get messy (e.g., database testing or when the
        # return contains a timestamp or using a closure 
        # computed when the arguments are constructed).

            [ blah_blah => ( 'a' .. 'z' ) ],
            'Validate blah_blah'

        # turn off verbosity


        # turn on/off a breakpoint prior to execution or if the
        # next step returns an error.


        # set a breakpoint via $DB::single = 1 prior to calling
        # $object->$method for all following tests.


            # for this one test: 
            # set a breakpoint after calling $object->$method 
            # iff $@ is true via $DB::single = 1 if $error;
            # also make this one test verbose.

            debug   =>
            verbose =>

            [ frobnicate => @frob_argz          ],
            [ 'eeny', 'meene', 'minie', 'moe'   ],
            [ "Frobnicate returns gibberish"    ]
            # YAML::XS has problems (a.k.a. segfaults) 
            # handling stored regexen. simplest workaround
            # is setting a flag to treat non-ref expect values
            # as bare regexen and feed them through qr{}x.

                regex =>
                YAPC =>
                "Title includes 'YAPC'"

    # stack tests: 
    # "noplan" skips calling "plan" with number of tests.
    # "nofinish" skips calling "done_testing" after current plan.
    # this leaves it up to the caller to call "done_testing"
    # or call exercise with "finish" set to true.

    $obj->$exercise ( qw( nofinish ) );

    $obj->$exercise( @plan1 );
    $obj->$exercise( @plan2 );
    $obj->$exercise( @plan3 );

    $obj->$exercise ( 'finish' );   # call's done testing.

    # You can push the operations through as
    # class or object methods.

    YourClass->$exercise( @test_opz );

    my $object = YourClass->new( @whatever );

    $object->$exercise( @test_opz );

    # or just

    YourClass->new( @blah )->$exercise( @test_opz );

    # sometimes it is simpler to pass the tests in as an arrayref
    # or as flat YAML text. A single arrayref on the stack will be
    # expanded in-place to get the tests, a single non-ref scalar
    # will be treated as YAML.
    # this makes it easy to store an arrayref as text or YAML in
    # the test body:

    my $plan    = do { local $/; eval <DATA> };
    $obj->$exercise( $plan );

    # or this could be a perly arrayref in Dumper format.

    - noplan
    - - verbose
      - - prepare_test
        - - get
        - - set_implicit_wait_timeout
          - 50000


This package exports a single subroutine , $exercise, which functions as an OO execution loop (see 'export' for changing the installed name).

$execute is a subroutine reference that takes an object and set of operations. The first element in that list is an object of the class being tested. The remaining elements are a list of operations, each of which is an array reference.

Each operation consists of a method call and the method's arguments. Each method call is dispatched using the object, optionally comparing the return value to some pre-defined result.

Exceptions are trapped and logged. The last operation can be re-executed if it fails.

All operations are passed in as arrayrefs. They can be nested either to store a return value and test to run, or to hold a list consisting of a method name and its arguments.

Arguments for "use Object::Exercise"

install=<yourname> (default "execute")

Default is to install '$execute', any alternate variable name can be selected.

benchmark (default 0)

This writes out the wallclock time to four decimal places (from Time::Hires) for each entry executed.

This can be set inline via [no]benchmark:

    [ ... ],

    # showing elapsed time for only one test:


    [ ... ],

verbose (default 0)

Turn on additinal progress messages, printing them to stderr so that they show up even if prove is not running in verbose mode.

This can be switched innline via "verbose" or "noverbose".

continue (default 1)

Continue execution after failures. Turning this off aborts after the first execption, which may interfere with test counts (see also "plan", next).

The main use of this is setting "nocontinue" in cases where some initial setup steps failing will force the remaining steps to fail.

plan (default 1)

Normally an initial count of the tests is used generate a test plan. If this is specified then no plan is used. This can be helpful when used with "nocontinue".

debug (default 0)

This sets a breakpoint if an execption is raised calling the method. The line following this breakpoint is:

    $obj->$method( @$argz );

which can be used to immediately check why a call failed.

Exercising Objects ^

The setup code for a typical test file is frequently repetitive. We have to code for the object and each of a collection of method calls. We frequently have to check return values and exception statuses.

This leads to blocks of code like this:

  my $obj = Package::New->( ... );

  if( defined ( my $return = eval { $obj->method_1( @args_1 ) } ) )
    @$return == 3 or die "...";

    cmp_deeply $return, [ ... ], "Failed comparing @argz_1: ...";

  elsif( $@ )
    die "Failed execution of method_1 ...";
    die "Undef returned from method_1 ..."

  eval { $obj->method_2( @args_2 ) };

  if( $@ )
    die "Failed execution of method_2 ...";

The only thing that really varies about any of these are the return values, method name, and arguments.

Object::Exercise reduces all of this to a list of methods and arguments, with optional data validation:

  [ method => @args ],      # single flat list in arrayref


    [ method => @args ]     # same method + arguments
    [ 3 ],                  # with added return value check

In both cases $@ is checked on return; in the second case Test::Deep::cmp_deeply is used to validate the returned data.

Test vs. Run-Only Operations

There are two types of operations: tests and run-only. Tests have a hard-coded value that is compared with the method call's return value; the return value of a run-only operation is ignored.


These are nested arrayrefs:

    [ $method => @args  ],
    [ expected return   ],
    'optional message'

The return value can be any sort of structure but must be enclosed in an arrayref. The test is run via:

  my $result = [ $object->$method( @argz ) ];

  cmp_deeply $result, $expected, $message;

This leaves any method called in a list context with the result put into an arryref. This means that the expected value for a call that returns arrayrefs will look like:

    [ $method => @argz ],
    [ # outer arrayref stored return value

      [ # return value is itself an arrayref ]

If the method returns hashrefs in list context then use something like:

    [ $method => @argz ],
        # outer arrayref stored return value
        # inner value is the hashref expected value.

      { ...  }

The default ok message is formed by joining the method and arguments on whitespace. This can lead to prove issuing lines like:

  ok save foobar HASH(0x123456) (999)

but usually gives at least recognizable results.

To override this, simply supply a message of your own:

    [ $method => @argz ],
    [ { # return value is itself an hashref } ],
    'Remember: This should return a hashref!'       # your message
Testing Known Failures

Sometimes it is useful to test how the code handles invalid requests. In these cases the test will fail. Normally, executing a method that returns with $@ set will be logged as a failed test. If the expected value is an empty array ref (i.e., nothing was expected back) then the $@ will be logged as passed.

These tests look like:

    [ qw( method designed to fail ) ]

    [ qw( method designed to fail ) ]

This will give a message like:

  ok save foobar HASH(0x123456) expected failure (999)
Run-Only Items

These consist simply of a method and its arguments:

  [ method => arg, arg, ...  ],

A method with no arguments is a one-liner:

  [ method ]

which leads to:


These are called in a void context, so if the method checks wantarray it will get undef. This may affect the execution of some methods, but usually will not (normal tests are wantarray ? a : b without the separate test for defined).


Coderef's are dispatched as standard method calls:

    my $coderef = sub { ... };  # or \&somesub

        [ $coderef, @argz ],
        [ ... ]

is executed as:

    $obj->$coderef( @argz )

this allows dispatching the object outside of its class, say to a utility function that does some extra data checking, logging, or updates the module. These are especially useful for updating the object state during execution.

Re-Running Failed Operations

Operations are deemed to fail if they raise an exception (i.e., $@ is set at their completion) or if the return value does not compare deeply to expected data (if provided).

In either case, it is often helpful to examine the failed operation. This is accomplished here by wrapping each exectution in a closure:

  my $cmd
  = sub
    $DB::single = 1 if $debug;

    $obj->$method( @argz )

These closures are eval-ed one at a time and then compared to expected values as necessary. If the operation raises an exception or the test fails then $debug is set to true and a breakpoint is set in the main loop. This allows code run in the perl debugger to re-execute the failed operation in single-step mode and see exactly what failed without having to single-step through all of the successful operations.

For example:

  perl -d harness_code.t;

will stop execution at the first failed operation, allowing a single s to step into the $obj->$method( @argz ) call.

Harness Directives

There are times when you want to control the execution or harness arguments as it is running. The directives are processed by the harness itself. These can set a breakpoint prior to calling one of the methods, adjust the verbosity, set the continue switch, or set an object value.


Sometimes it's reassuring to know progress is being make (or it's helpful to keep a log of what happend).

Non-referent entries in the test list that aren't recognized are simply printed:


    "Updating based on $computed value...",

        [ foobar  => $computed_value ],

    "... Finished Computed value update.",

will sandwich a method call between two messages.


It is sometimes helpful to stop the execution of code before it fails in order to examine its execution before the failure. The "break" directive will set the breakpoint before the first method call. This will leave you at $obj->$method( @argz ) (see below under DEBUGGING).

For example, this will run up to the point where "frobnicate" is about to be called and then stop:



      [ qw( frobnicate foo ) ],
      [ 3 ],


This leaves the perl debugger at the line:

    my $result = [ $obj->$method( @$argz ) ];

Until "nobreak" is used all calls will hit the breakpoint.

Turning off comparison breakpoints.

Normal behavior for Object::Exercise is to abort the execution plan when the first $@ or cmp_deeply failure is encountered. The behavior can be changed to continue execution via the "continue" directive (or set via the "-k" switch when the module is used). Inserting "nocontinue" will turn back on the normal behavior.

This can be helpful when initial operations need to clean up before starting: failures can be ignored until some set of sanity checks.


    [ cleanup that may fail.  ],
    [ cleanup that may fail.  ],


    [ sanity check ]

Execution will log any failures through the "nocontinue" line as expected failures, something like:

  ok 1 - modify label field_x xyz => xyz
  ok 2 - lookup label field_x => xyz
* ok 3 - modify label field_x => expected exception
  ok 4 - lookup label field_x => xyz


Re-run a failed operation:

  $ perl -d ./t/some-test.t;

  ok ...
  ok ...
  ok ...


  Failed execution:
  <failure message>

  47:       0
    DB<1> &$cmd

  184:              $obj->$method( @argz )
    DB<<2>> s

At this point you will be at the first line of $method (given sub or coderef location). The failure message will show up for $@ set after calling the method or if cmp_deeply finds a discrepency in the result.


Aside: Yes I know we need more of these...

    my $field2 = 'field_x';

    my @opz =
        # evaluate expected failures

        # modify is expected to fail, but the empty
        # arrayref is a signal that nothing is expected
        # back from the test.

            [ drop =>   ( $field_2 ) ],                 # pre-cleanup
            ''                                          # ignore failre

            [ write =>  ( label => $field2, 'xyz' ) ],
            [ 'xyz'                                 ],  # expect 'xyz'

            [ read =>   ( label => $field2 )        ],
            [ qw( xyz )                             ],  # expect 'xyz'

            [ write =>  ( label => $field2, '' )    ],  # invalid argument:
            '',                                         # expect failure

            [ read =>   ( label => $field2 )        ],
            [ qw( xyz )                             ],  # expect 'xyz'


    $execute->( $object, @opz );


Steven Lembark <>


Copyright (C) 2007-2015 Steven Lembark. This code is released under the same terms as Perl-5.22 or any later version of Perl.

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