X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=moose-class%2Fexercises%2Ft%2Flib%2FMooseClass%2FTests.pm;h=b6de65d8d663dd70c29e7f5b0ab3ebac2675ec9a;hb=75a3a97a5e79d6cc099193e14c575c9c84085ded;hp=5455a27dddbb289f8e90b2ffafca321f3807eb2f;hpb=8d1ce1d704a422c266cc8d3a5a50c98c2a25fc38;p=gitmo%2Fmoose-presentations.git

diff --git a/moose-class/exercises/t/lib/MooseClass/Tests.pm b/moose-class/exercises/t/lib/MooseClass/Tests.pm
index 5455a27..b6de65d 100644
--- a/moose-class/exercises/t/lib/MooseClass/Tests.pm
+++ b/moose-class/exercises/t/lib/MooseClass/Tests.pm
@@ -4,118 +4,401 @@ use strict;
 use warnings;
 
 use Lingua::EN::Inflect qw( A PL_N );
+use Scalar::Util qw( blessed );
 use Test::More 'no_plan';
 
 sub tests01 {
-    my %p = (
-        person_attr_count   => 2,
-        employee_attr_count => 3,
-        @_,
-    );
-
-    local $Test::Builder::Level = $Test::Builder::Level + 1;
-
     has_meta('Person');
 
     check_isa( 'Person', ['Moose::Object'] );
 
-    count_attrs( 'Person', $p{person_attr_count} );
-
     has_rw_attr( 'Person', $_ ) for qw( first_name last_name );
 
     has_method( 'Person', 'full_name' );
 
-    no_droppings('Person');
-    is_immutable('Person');
-
     person01();
 
     has_meta('Employee');
 
     check_isa( 'Employee', [ 'Person', 'Moose::Object' ] );
 
-    count_attrs( 'Employee', $p{employee_attr_count} );
-
     has_rw_attr( 'Employee', $_ ) for qw( title salary );
     has_ro_attr( 'Employee', 'ssn' );
 
     has_overridden_method( 'Employee', 'full_name' );
 
     employee01();
+
+    no_droppings('Person');
+    is_immutable('Person');
+
+    no_droppings('Employee');
+    is_immutable('Employee');
 }
 
 sub tests02 {
-    tests01( person_attr_count => 3, @_ );
+    has_meta('Printable');
+    requires_method( 'Printable', 'as_string' );
 
-    local $Test::Builder::Level = $Test::Builder::Level + 1;
+    has_meta('Person');
+    does_role( 'Person', 'Printable' );
+    has_method( 'Person', 'as_string' );
 
-    no_droppings($_) for qw( Printable HasAccount );
+    has_meta('HasAccount');
+    has_method( 'HasAccount', $_ ) for qw( deposit withdraw );
+    has_role_attr( 'HasAccount', 'balance' );
 
-    does_role( 'Person', $_ ) for qw( Printable HasAccount );
-    has_method( 'Person', $_ ) for qw( as_string deposit withdraw );
+    does_role( 'Person', 'HasAccount' );
+    has_method( 'Person', $_ ) for qw( deposit withdraw );
     has_rw_attr( 'Person', 'balance' );
 
+    has_meta('Employee');
     does_role( 'Employee', $_ ) for qw( Printable HasAccount );
 
     person02();
     employee02();
-}
 
-sub tests03 {
-    {
-        local $Test::Builder::Level = $Test::Builder::Level + 1;
+    no_droppings($_) for qw( Printable HasAccount );
 
-        has_meta('Person');
-        has_meta('Employee');
+    tests01();
+}
 
-        has_rw_attr( 'Person', 'title' );
+sub tests03 {
+    has_meta('Person');
 
-        has_rw_attr( 'Employee', 'title' );
-        has_rw_attr( 'Employee', 'salary_level' );
-        has_ro_attr( 'Employee', 'salary' );
+    for my $name ( qw( first_name last_name ) ) {
+        has_rw_attr( 'Person', $name );
 
-        has_method( 'Employee', '_build_salary' );
+        my $attr = Person->meta->get_attribute($name);
+        ok( $attr && $attr->is_required,
+            "$name is required in Person" );
     }
 
-    ok( ! Employee->meta->has_method('full_name'),
-        'Employee no longer implements a full_name method' );
+    has_rw_attr( 'Person', 'title' );
 
     my $person_title_attr = Person->meta->get_attribute('title');
     ok( !$person_title_attr->is_required, 'title is not required in Person' );
-    is( $person_title_attr->predicate, 'has_title',
-        'Person title attr has a has_title predicate' );
-    is( $person_title_attr->clearer, 'clear_title',
-        'Person title attr has a clear_title clearer' );
+    is(
+        $person_title_attr->predicate, 'has_title',
+        'Person title attr has a has_title predicate'
+    );
+    is(
+        $person_title_attr->clearer, 'clear_title',
+        'Person title attr has a clear_title clearer'
+    );
 
-    my $balance_attr = Person->meta->get_attribute('balance');
-    is( $balance_attr->default, 100, 'balance defaults to 100' );
+    person03();
+
+    has_meta('Employee');
+
+    has_rw_attr( 'Employee', 'title', 'overridden' );
 
     my $employee_title_attr = Employee->meta->get_attribute('title');
-    is( $employee_title_attr->default, 'Worker',
-        'title defaults to Worker in Employee' );
+    is(
+        $employee_title_attr->default, 'Worker',
+        'title defaults to Worker in Employee'
+    );
 
-    my $salary_level_attr = Employee->meta->get_attribute('salary_level');
-    is( $salary_level_attr->default, 1, 'salary_level defaults to 1' );
+    ok(
+        !Employee->meta->has_method('full_name'),
+        'Employee no longer implements a full_name method'
+    );
+
+    has_ro_attr( 'Employee', 'salary' );
 
     my $salary_attr = Employee->meta->get_attribute('salary');
+    ok( $salary_attr->is_lazy, 'salary is lazy' );
     ok( !$salary_attr->init_arg,   'no init_arg for salary attribute' );
     ok( $salary_attr->has_builder, 'salary attr has a builder' );
 
-    person03();
+    has_method( 'Employee', '_build_salary' );
+
+    has_rw_attr( 'Employee', 'salary_level' );
+
+    my $salary_level_attr = Employee->meta->get_attribute('salary_level');
+    is( $salary_level_attr->default, 1, 'salary_level defaults to 1' );
+
     employee03();
+
+    my $balance_attr = Person->meta->get_attribute('balance');
+    is( $balance_attr->default, 100, 'balance defaults to 100' );
+}
+
+sub tests04 {
+    has_meta('Person');
+
+    ok( Person->can('full_name'), 'Person has a full_name() method' )
+        or BAIL_OUT(
+        'Person does not have a full_name() method. Cannot continue testing.'
+        );
+
+    my $meth = Person->meta()->get_method('full_name');
+    ok(
+        $meth && $meth->isa('Class::MOP::Method::Wrapped'),
+        'method modifiers have been applied to the Person->full_name method'
+    );
+
+    is(
+        scalar $meth->before_modifiers,
+        1,
+        'Person->full_name has a single before modifier'
+    );
+
+    is(
+        scalar $meth->after_modifiers,
+        1,
+        'Person->full_name has a single after modifier'
+    );
+
+    my $person = Person->new(
+        first_name => 'Bilbo',
+        last_name  => 'Baggins',
+    );
+
+    is_deeply(
+        \@Person::CALL,
+        [],
+        'Person::CALL global is empty before calling full_name'
+    );
+
+    $person->full_name();
+
+    is_deeply(
+        \@Person::CALL,
+        [ 'calling full_name', 'called full_name' ],
+        'Person::CALL global contains before and after strings'
+    );
+
+    is(
+        scalar $meth->around_modifiers,
+        1,
+        'Person->full_name has a single around modifier'
+    );
+
+    my $larry = Person->new(
+        first_name => 'Larry',
+        last_name  => 'Wall',
+    );
+
+    is(
+        $larry->full_name,
+        '*Larry Wall*',
+        'full_name is wrapped by asterisks when last name is Wall'
+    );
+}
+
+sub tests05 {
+    has_meta('Person');
+
+    for my $attr_name (qw( first_name last_name title )) {
+        my $attr = Person->meta->get_attribute($attr_name);
+
+        ok(
+            $attr->has_type_constraint,
+            "Person $attr_name has a type constraint"
+        );
+        is(
+            $attr->type_constraint->name, 'Str',
+            "Person $attr_name type is Str"
+        );
+    }
+
+    has_meta('Employee');
+
+    {
+        my $salary_level_attr = Employee->meta->get_attribute('salary_level');
+        ok(
+            $salary_level_attr->has_type_constraint,
+            'Employee salary_level has a type constraint'
+        );
+
+        my $tc = $salary_level_attr->type_constraint;
+
+        for my $invalid ( 0, 11, -14, 'foo', undef ) {
+            my $str = defined $invalid ? $invalid : 'undef';
+            ok(
+                !$tc->check($invalid),
+                "salary_level type rejects invalid value - $str"
+            );
+        }
+
+        for my $valid ( 1 .. 10 ) {
+            ok(
+                $tc->check($valid),
+                "salary_level type accepts valid value - $valid"
+            );
+        }
+    }
+
+    {
+        my $salary_attr = Employee->meta->get_attribute('salary');
+
+        ok(
+            $salary_attr->has_type_constraint,
+            'Employee salary has a type constraint'
+        );
+
+        my $tc = $salary_attr->type_constraint;
+
+        for my $invalid ( 0, -14, 'foo', undef ) {
+            my $str = defined $invalid ? $invalid : 'undef';
+            ok(
+                !$tc->check($invalid),
+                "salary type rejects invalid value - $str"
+            );
+        }
+
+        for my $valid ( 1, 100_000, 10**10 ) {
+            ok(
+                $tc->check($valid),
+                "salary type accepts valid value - $valid"
+            );
+        }
+    }
+
+    {
+        my $ssn_attr = Employee->meta->get_attribute('ssn');
+
+        ok(
+            $ssn_attr->has_type_constraint,
+            'Employee ssn has a type constraint'
+        );
+
+        my $tc = $ssn_attr->type_constraint;
+
+        for my $invalid ( 0, -14, 'foo', undef, '123-ab-1241', '123456789' ) {
+            my $str = defined $invalid ? $invalid : 'undef';
+            ok(
+                !$tc->check($invalid),
+                "ssn type rejects invalid value - $str"
+            );
+        }
+
+        for my $valid ( '041-12-1251', '123-45-6789', '926-41-5820' ) {
+            ok(
+                $tc->check($valid),
+                "ssn type accepts valid value - $valid"
+            );
+        }
+    }
+
+    no_droppings('Employee');
+}
+
+sub tests06 {
+    has_meta('BankAccount');
+
+    has_rw_attr( 'BankAccount', $_ ) for qw( balance owner );
+
+    my $ba_meta = BankAccount->meta;
+
+    ok(
+        $ba_meta->get_attribute('owner')->is_weak_ref,
+        'owner attribute is a weak ref'
+    );
+
+    has_method( 'BankAccount', $_ ) for qw( deposit withdraw );
+
+    has_ro_attr( 'BankAccount', 'history' );
+
+    my $history_attr = $ba_meta->get_attribute('history');
+
+    is_deeply(
+        $history_attr->default->(),
+        [],
+        'BankAccount history attribute defaults to []'
+    );
+
+    {
+        my $tc = $history_attr->type_constraint;
+
+        for my $invalid ( 0, 42, undef, {}, [ 'foo', 'bar' ] ) {
+            my $str = defined $invalid ? $invalid : 'undef';
+            ok(
+                !$tc->check($invalid),
+                "salary_level type rejects invalid value - $str"
+            );
+        }
+
+        for my $valid ( [], [1], [ 1, 2, 3 ], [ 1, -10, 9999 ] ) {
+            ok(
+                $tc->check($valid),
+                "salary_level type accepts valid value"
+            );
+        }
+    }
+
+    ok(
+        $history_attr->meta()->can('does_role')
+            && $history_attr->meta()
+            ->does_role('Moose::Meta::Attribute::Native::Trait::Array'),
+        'BankAccount history attribute uses native delegation to an array ref'
+    );
+
+    ok(
+        $ba_meta->get_attribute('balance')->has_trigger,
+        'BankAccount balance attribute has a trigger'
+    );
+
+    has_meta('Person');
+
+    my $person_meta = Person->meta;
+
+    ok( !$person_meta->does_role('HasAccount'),
+        'Person class does not do the HasAccount role' );
+
+    ok(
+        !$person_meta->has_attribute('balance'),
+        'Person class does not have a balance attribute'
+    );
+
+    my $deposit_meth = $person_meta->get_method('deposit');
+    _my_isa_ok(
+        $deposit_meth, 'Moose::Meta::Method::Delegation',
+        'The Person->deposit method exists and is a delegation method'
+    );
+
+    my $withdraw_meth = $person_meta->get_method('withdraw');
+    _my_isa_ok(
+        $withdraw_meth, 'Moose::Meta::Method::Delegation',
+        'The Person->withdraw method exists and is a delegation method'
+    );
+
+    person06();
+
+    has_meta('Employee');
+
+    no_droppings('BankAccount');
 }
 
 sub has_meta {
-    my $class = shift;
+    my $package = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    {
+        my @warn;
+        local $SIG{__WARN__} = sub { push @warn, @_ };
+
+        use_ok($package)
+            or BAIL_OUT("$package cannot be loaded");
+
+        BAIL_OUT("Warning when loading $package: @warn")
+            if @warn;
+    }
 
-    ok( $class->can('meta'), "$class has a meta() method" )
-        or BAIL_OUT("Cannot run tests against a class without a meta!");
+    ok( $package->can('meta'), "$package has a meta() method" )
+        or BAIL_OUT(
+        "$package does not have a meta() method (did you forget to 'use Moose'?)"
+        );
 }
 
 sub check_isa {
     my $class   = shift;
     my $parents = shift;
 
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
     my @isa = $class->meta->linearized_isa;
     shift @isa;    # returns $class as the first entry
 
@@ -129,83 +412,131 @@ sub check_isa {
     }
 }
 
-sub count_attrs {
-    my $class = shift;
-    my $count = shift;
-
-    my $noun = PL_N( 'attribute', $count );
-    is( scalar $class->meta->get_attribute_list, $count,
-        "$class defines $count $noun" );
-}
-
 sub has_rw_attr {
-    my $class = shift;
-    my $name  = shift;
+    my $class      = shift;
+    my $name       = shift;
+    my $overridden = shift;
 
-    my $articled = A($name);
-    ok( $class->meta->has_attribute($name),
-        "$class has $articled attribute" );
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    my $articled = $overridden ? "an overridden $name" : A($name);
+    ok(
+        $class->meta->has_attribute($name),
+        "$class has $articled attribute"
+    );
 
     my $attr = $class->meta->get_attribute($name);
 
-    is( $attr->get_read_method, $name,
-        "$name attribute has a reader accessor - $name()" );
-    is( $attr->get_write_method, $name,
-        "$name attribute has a writer accessor - $name()" );
+    is(
+        $attr->get_read_method, $name,
+        "$name attribute has a reader accessor - $name()"
+    );
+    is(
+        $attr->get_write_method, $name,
+        "$name attribute has a writer accessor - $name()"
+    );
 }
 
 sub has_ro_attr {
     my $class = shift;
     my $name  = shift;
 
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
     my $articled = A($name);
-    ok( $class->meta->has_attribute($name),
-        "$class has $articled attribute" );
+    ok(
+        $class->meta->has_attribute($name),
+        "$class has $articled attribute"
+    );
 
     my $attr = $class->meta->get_attribute($name);
 
-    is( $attr->get_read_method, $name,
-        "$name attribute has a reader accessor - $name()" );
-    is( $attr->get_write_method, undef,
-        "$name attribute does not have a writer" );
+    is(
+        $attr->get_read_method, $name,
+        "$name attribute has a reader accessor - $name()"
+    );
+    is(
+        $attr->get_write_method, undef,
+        "$name attribute does not have a writer"
+    );
+}
+
+sub has_role_attr {
+    my $role = shift;
+    my $name = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    my $articled = A($name);
+    ok(
+        $role->meta->get_attribute($name),
+        "$role has $articled attribute"
+    );
 }
 
 sub has_method {
-    my $class = shift;
-    my $name  = shift;
+    my $package = shift;
+    my $name    = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
 
     my $articled = A($name);
-    ok( $class->meta->has_method($name), "$class has $articled method" );
+    ok( $package->meta->has_method($name), "$package has $articled method" );
 }
 
 sub has_overridden_method {
-    my $class = shift;
-    my $name  = shift;
+    my $package = shift;
+    my $name    = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
 
     my $articled = A($name);
-    ok( $class->meta->has_method($name), "$class has $articled method" );
+    ok( $package->meta->has_method($name), "$package has $articled method" );
+
+    my $meth = $package->meta->get_method($name);
+    _my_isa_ok(
+        $meth, 'Moose::Meta::Method::Overridden',
+        "The $name method is an overridden method"
+    );
+}
 
-    my $meth = $class->meta->get_method($name);
-    isa_ok( $meth, 'Moose::Meta::Method::Overridden' );
+sub requires_method {
+    my $package = shift;
+    my $method  = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    ok(
+        $package->meta->requires_method($method),
+        "$package requires the method $method"
+    );
 }
 
 sub no_droppings {
-    my $class = shift;
+    my $package = shift;
 
-    ok( !$class->can('has'), "no Moose droppings in $class" );
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    ok( !$package->can('has'), "no Moose droppings in $package" );
+    ok( !$package->can('subtype'),
+        "no Moose::Util::TypeConstraints droppings in $package" );
 }
 
 sub is_immutable {
     my $class = shift;
 
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
     ok( $class->meta->is_immutable, "$class has been made immutable" );
 }
 
 sub does_role {
-    my $class = shift;
-    my $role  = shift;
+    my $package = shift;
+    my $role    = shift;
+
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
 
-    ok( $class->meta->does_role($role), "$class does the $role role" );
+    ok( $package->meta->does_role($role), "$package does the $role role" );
 }
 
 sub person01 {
@@ -214,8 +545,35 @@ sub person01 {
         last_name  => 'Baggins',
     );
 
-    is( $person->full_name, 'Bilbo Baggins',
-        'full_name() is correctly implemented' );
+    is(
+        $person->full_name, 'Bilbo Baggins',
+        'full_name() is correctly implemented'
+    );
+
+    $person = eval { Person->new( [ qw( Lisa Smith ) ] ) };
+
+    if ( my $e = $@ ) {
+        diag(
+            "Calling Person->new() with an array reference threw an error:\n$e"
+        );
+        BAIL_OUT(
+            'You must implement Person->BUILDARGS correctly in order to continue these tests'
+        );
+    }
+    else {
+        ok( 1, 'Person->new() can accept an array reference as an argument' );
+    }
+
+    is( $person->first_name, 'Lisa', 'set first_name from two-arg arrayref' );
+    is( $person->last_name, 'Smith', 'set last_name from two-arg arrayref' );
+
+    eval {
+        Person->new( sub {'foo'} );
+    };
+    like(
+        $@, qr/\QSingle parameters to new() must be a HASH ref/,
+        'Person constructor still rejects bad parameters'
+    );
 }
 
 sub employee01 {
@@ -225,7 +583,16 @@ sub employee01 {
         title      => 'Singer',
     );
 
-    is(        $employee->full_name, 'Amanda Palmer (Singer)',        'full_name() is properly overriden in Employee'    );
+    my $called     = 0;
+    my $orig_super = \&Employee::super;
+    no warnings 'redefine';
+    local *Employee::super = sub { $called++; goto &$orig_super };
+
+    is(
+        $employee->full_name, 'Amanda Palmer (Singer)',
+        'full_name() is properly overriden in Employee'
+    );
+    ok( $called, 'Employee->full_name calls super()' );
 }
 
 sub person02 {
@@ -235,8 +602,10 @@ sub person02 {
         balance    => 0,
     );
 
-    is( $person->as_string, 'Bilbo Baggins',
-        'as_string() is correctly implemented' );
+    is(
+        $person->as_string, 'Bilbo Baggins',
+        'as_string() is correctly implemented'
+    );
 
     account_tests($person);
 }
@@ -249,8 +618,10 @@ sub employee02 {
         balance    => 0,
     );
 
-    is( $employee->as_string, 'Amanda Palmer (Singer)',
-        'as_string() uses overridden full_name method in Employee' );
+    is(
+        $employee->as_string, 'Amanda Palmer (Singer)',
+        'as_string() uses overridden full_name method in Employee'
+    );
 
     account_tests($employee);
 }
@@ -261,15 +632,30 @@ sub person03 {
         last_name  => 'Baggins',
     );
 
-    is( $person->full_name, 'Bilbo Baggins',
-        'full_name() is correctly implemented for a Person without a title' );
-    ok( !$person->has_title,
-        'Person has_title predicate is working correctly' );
+    is(
+        $person->full_name, 'Bilbo Baggins',
+        'full_name() is correctly implemented for a Person without a title'
+    );
+    ok(
+        !$person->has_title,
+        'Person has_title predicate is working correctly (returns false)'
+    );
 
     $person->title('Ringbearer');
-    ok( $person->has_title, 'Person has_title predicate is working correctly' );
-    is( $person->full_name, 'Bilbo Baggins (Ringbearer)',
-        'full_name() is correctly implemented for a Person with a title' );
+    ok( $person->has_title,
+        'Person has_title predicate is working correctly (returns true)' );
+
+    my $called    = 0;
+    my $orig_pred = \&Person::has_title;
+    no warnings 'redefine';
+    local *Person::has_title = sub { $called++; goto &$orig_pred };
+
+    is(
+        $person->full_name, 'Bilbo Baggins (Ringbearer)',
+        'full_name() is correctly implemented for a Person with a title'
+    );
+    ok( $called,
+        'full_name in person uses the predicate for the title attribute' );
 
     $person->clear_title;
     ok( !$person->has_title, 'Person clear_title method cleared the title' );
@@ -285,8 +671,53 @@ sub employee03 {
         salary       => 42,
     );
 
-    is( $employee->salary, 30000,
-        'salary is calculated from salary_level, and salary passed to constructor is ignored' );
+    is(
+        $employee->salary, 30000,
+        'salary is calculated from salary_level, and salary passed to constructor is ignored'
+    );
+}
+
+sub person06 {
+    my $account = BankAccount->new();
+
+    my $person = Person->new(
+        first_name => 'Bilbo',
+        last_name  => 'Baggins',
+        account    => $account,
+    );
+
+    is(
+        $person->account, $account,
+        'account object passed to Person->new is still in object'
+    );
+
+    _my_isa_ok(
+        $person->account, 'BankAccount',
+        'The value of $person->account() isa BankAccount object'
+    );
+
+    is(
+        $person->account->owner, $person,
+        'owner of bank account is person that created account'
+    );
+
+    $person->deposit(10);
+    is_deeply(
+        $person->account->history, [100],
+        'deposit was recorded in account history'
+    );
+
+    $person->withdraw(15);
+    is_deeply(
+        $person->account->history, [ 100, 110 ],
+        'withdrawal was recorded in account history'
+    );
+
+    $person->withdraw(45);
+    is_deeply(
+        $person->account->history, [ 100, 110, 95 ],
+        'withdrawal was recorded in account history'
+    );
 }
 
 sub account_tests {
@@ -296,14 +727,37 @@ sub account_tests {
     my $base_amount = shift || 0;
 
     $person->deposit(50);
+
+    is(
+        $person->balance, 50 + $base_amount,
+        "balance is 50 + $base_amount",
+    );
+
     eval { $person->withdraw( 75 + $base_amount ) };
-    like( $@, qr/\QBalance cannot be negative/,
-          'cannot withdraw more than is in our balance' );
+    like(
+        $@, qr/\QBalance cannot be negative/,
+        'cannot withdraw more than is in our balance'
+    );
+
+    $person->withdraw(23);
 
-    $person->withdraw( 23 );
+    is(
+        $person->balance, 27 + $base_amount,
+        'balance is 27 (+ starting balance) after deposit of 50 and withdrawal of 23'
+    );
+}
+
+sub _my_isa_ok {
+    my $thing = shift;
+    my $class = shift;
+    my $desc  = shift;
 
-    is( $person->balance, 27 + $base_amount,
-        'balance is 27 (+ starting balance) after deposit of 50 and withdrawal of 23' );
+    local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+    ok(
+        $thing && ( blessed $thing || !ref $thing ) && $thing->isa($class),
+        $desc
+    );
 }
 
 1;