NAME¶
Test::Deep - Extremely flexible deep comparison
SYNOPSIS¶
use Test::More tests => $Num_Tests;
use Test::Deep;
cmp_deeply(
$actual_horrible_nested_data_structure,
$expected_horrible_nested_data_structure,
"got the right horrible nested data structure"
);
cmp_deeply(
$object,
methods(name => "John", phone => "55378008"),
"object methods ok"
);
cmp_deeply(
\@array,
[$hash1, $hash2, ignore()],
"first 2 elements are as expected, ignoring 3"
);
cmp_deeply(
$object,
noclass({value => 5}),
"object looks ok, not checking it's class"
);
cmp_deeply(
\@result,
bag('a', 'b', {key => [1, 2]}),
"array has the 3 things we wanted in some order"
);
DESCRIPTION¶
If you don't know anything about automated testing in Perl then you should
probably read about Test::Simple and Test::More before preceding. Test::Deep
uses the Test::Builder framework.
Test::Deep gives you very flexible ways to check that the result you got is the
result you were expecting. At it's simplest it compares two structures by
going through each level, ensuring that the values match, that arrays and
hashes have the same elements and that references are blessed into the correct
class. It also handles circular data structures without getting caught in an
infinite loop.
Where it becomes more interesting is in allowing you to do something besides
simple exact comparisons. With strings, the "eq" operator checks
that 2 strings are exactly equal but sometimes that's not what you want. When
you don't know exactly what the string should be but you do know some things
about how it should look, "eq" is no good and you must use pattern
matching instead. Test::Deep provides pattern matching for complex data
structures
EXAMPLES¶
How Test::Deep works is much easier to understand by seeing some examples.
Without Test::Deep¶
Say you want to test a function which returns a string. You know that your
string should be a 7 digit number beginning with 0, "eq" is no good
in this situation, you need a regular expression. So you could use
Test::More's "like()" function:
like($string, '/^0d{6}$/', "number looks good");
Similarly, to check that a string looks like a name, you could do:
like($string, '/^(Mr|Mrs|Miss) \w+ \w+$/',
"got title, first and last name");
Now imagine your function produces a hash with some personal details in it. You
want to make sure that there are 2 keys, Name and Phone and that the name
looks like a name and the phone number looks like a phone number. You could
do:
$hash = make_person();
like($hash->{Name}, '/^(Mr|Mrs|Miss) \w+ \w+$/', "name ok");
like($hash->{Phone}, '/^0d{6}$/', "phone ok");
is(scalar keys %$hash, 2, "correct number of keys");
But that's not quite right, what if make_person has a serious problem and didn't
even return a hash? We really need to write
if (ref($hash) eq "HASH")
{
like($hash->{Name}, '/^(Mr|Mrs|Miss) \w+ \w+$/', "name ok");
like($hash->{Phone}, '/^0d{6}$/', "phone ok");
is(scalar keys %$hash, 2, "correct number of keys");
}
else
{
fail("person not a hash");
fail("person not a hash");
fail("person not a hash"); # need 3 to keep the plan correct
}
Already this is getting messy, now imagine another entry in the hash, an array
of children's names. This would require
if (ref($hash) eq "HASH")
{
like($hash->{Name}, $name_pat, "name ok");
like($hash->{Phone}, '/^0d{6}$/', "phone ok");
my $cn = $hash->{ChildNames};
if (ref($cn) eq "ARRAY")
{
foreach my $child (@$cn)
{
like($child, $name_pat);
}
}
else
{
fail("child names not an array")
}
}
else
{
fail("person not a hash");
}
This is a horrible mess and because we don't know in advance how many children's
names there will be, we can't make a plan for our test anymore (actually, we
could but it would make things even more complicated).
Test::Deep to the rescue.
With Test::Deep¶
my $name_re = re('^(Mr|Mrs|Miss) \w+ \w+$');
cmp_deeply(
$person,
{
Name => $name_re,
Phone => re('^0d{6}$'),
ChildNames => array_each($name_re)
},
"person ok"
);
This will do everything that the messy code above does and it will give a
sensible message telling you exactly what went wrong if it finds a part of
$person that doesn't match the pattern. "re()" and
"array_each()" are special function imported from Test::Deep. They
create a marker that tells Test::Deep that something different is happening
here. Instead of just doing a simple comparison and checking are two things
exactly equal, it should do something else.
If a person was asked to check that 2 structures are equal, they could print
them both out and compare them line by line. The markers above are similar to
writing a note in red pen on one of the printouts telling the person that for
this piece of the structure, they should stop doing simple line by line
comparison and do something else.
"re($regex)" means that Test::Deep should check that the current piece
of data matches the regex in $regex. "array_each($struct)" means
that Test::Deep should expect the current piece of data to be an array and it
should check that every element of that array matches $struct. In this case,
every element of "$person->{ChildNames}" should look like a name.
If say the 3rd one didn't you would get an error message something like
Using Regexp on $data->{ChildNames}[3]
got : 'Queen John Paul Sartre'
expect : /^(Mr|Mrs|Miss) \w+ \w+$/
There are lots of other special comparisons available, see "SPECIAL
COMPARISONS PROVIDED" below for the full list.
Reusing structures¶
Test::Deep is good for reusing test structures so you can do this
my $name_re = re('^(Mr|Mrs|Miss) \w+ \w+$');
my $person_cmp = {
Name => $name_re,
Phone => re('^0d{6}$'),
ChildNames => array_each($name_re)
};
cmp_deeply($person1, $person_cmp, "person ok");
cmp_deeply($person2, $person_cmp, "person ok");
cmp_deeply($person3, $person_cmp, "person ok");
You can even put $person_cmp in a module and let other people use it when they
are writing test scripts for modules that use your modules.
To make things a little more difficult, lets change the person data structure so
that instead of a list of ChildNames, it contains a list of hashes, one for
each child. So in fact our person structure will contain other person
structures which may contain other person structures and so on. This is easy
to handle with Test::Deep because Test::Deep structures can include
themselves. Simply do
my $name_re = re('^(Mr|Mrs|Miss) \w+ \w+$');
my $person_cmp = {
Name => $name_re,
Phone => re('^0d{6}$'),
# note no mention of Children here
};
$person_cmp->{Children} = array_each($person_cmp);
cmp_deeply($person, $person_cmp, "person ok");
This will now check that $person->{Children} is an array and that every
element of that array also matches $person_cmp, this includes checking that
it's children also match the same pattern and so on.
Circular data structures¶
A circular data structure is one which loops back on itself, you can make one
easily by doing
my @b;
my @a = (1, 2, 3, \@b);
push(@b, \@a);
now @a contains a reference to be @b and @b contains a reference to @a. This
causes problems if you have a program that wants to look inside @a and keep
looking deeper and deeper at every level, it could get caught in an infinite
loop looking into @a then @b then @a then @b and so on.
Test::Deep avoids this problem so we can extend our example further by saying
that a person should also list their parents.
my $name_re = re('^(Mr|Mrs|Miss) \w+ \w+$');
my $person_cmp = {
Name => $name_re,
Phone => re('^0d{6}$'),
# note no mention of Children here
};
$person_cmp->{Children} = each_array($person_cmp);
$person_cmp->{Parents} = each_array($person_cmp);
cmp_deeply($person, $person_cmp, "person ok");
So this will check that for each child $child in
"$person->{Children}" that the "$child->{Parents}"
matches $person_cmp however it is smart enough not to get caught in an
infinite loop where it keeps bouncing between the same Parent and Child.
TERMINOLOGY¶
"cmp_deeply($got, $expected, $name)" takes 3 arguments. $got is the
structure that you are checking, you must not include any special comparisons
in this structure or you will get a fatal error. $expected describes what
Test::Deep will be looking for in $got. You can put special comparisons in
$expected if you want to.
As Test::Deep descends through the 2 structures, it compares them one piece at a
time, so at any point in the process, Test::Deep is thinking about 2 things -
the current value from $got and the current value from $expected. In the
documentation, I call them $got_v and "exp_v" respectively.
COMPARISON FUNCTIONS¶
$ok = cmp_deeply($got, $expected,
$name )
$got is the result to be checked. $expected is the structure against which $got
will be check. $name is the test name.
This is the main comparison function, the others are just wrappers around this.
Without any special comparisons, it will descend into $expected, following
every reference and comparing $expected_v to $got_v (using "eq") at
the same position. If at any stage $expected_v is a special comparison then
Test::Deep may do something else besides a simple string comparison, exactly
what it does depends on which special comparison it is.
$ok = cmp_bag(\@got, \@bag, $name)
Is shorthand for cmp_deeply(\@got, bag(@bag), $name)
N.B. Both arguments must be array refs. If they aren't an error will be raised
via die.
$ok = cmp_set(\@got, \@set, $name)
Is shorthand for cmp_deeply(\@got, set(@set), $name)
$ok = cmp_methods(\@got, \@methods, $name)
Is shorthand for cmp_deeply(\@got, methods(@methods), $name)
$ok = eq_deeply($got, $expected)
This is the same as
cmp_deeply() except it just returns true or false. It
does not create diagnostics or talk to Test::Builder, but if you want to use
it in a non-testing environment then you should import it through
Test::Deep::NoTest. For example
use Test::Deep::NoTest;
print "a equals b" unless eq_deeply($a, $b);
otherwise the Test::Builder framework will be loaded and testing messages will
be output when your program ends.
($ok, $stack) = cmp_details($got, $expected)
This behaves much like eq_deeply, but it additionally allows you to produce
diagnostics in case of failure by passing the value in $stack to
"deep_diag".
Do not make assumptions about the structure or content of $stack and do not use
it if $ok contains a true value.
See "USING TEST::DEEP WITH TEST::BUILDER" for example uses.
SPECIAL COMPARISONS PROVIDED¶
ignore()
This makes Test::Deep skip tests on $got_v. No matter what value $got_v has,
Test::Deep will think it's correct. This is useful if some part of the
structure you are testing is very complicated and already tested elsewhere, or
is unpredictable.
cmp_deeply($got, { name => 'John', random => ignore(), address => ['5 A
street', 'a town', 'a country'],
})
is the equivalent of checking
$got->{name} eq 'John';
exists $got->{random};
cmp_deeply($got->{address};
['5 A street', 'a town', 'a country']);
methods(%hash)
%hash is a hash of method call => expected value pairs.
This lets you call methods on an object and check the result of each call. The
methods will be called in the order supplied. If you want to pass arguments to
the method you should wrap the method name and arguments in an array
reference.
cmp_deeply(
$obj,
methods(name => "John", ["favourite", "food"] => "taco")
);
is roughly the equivalent of checking that
$obj->name eq "John"
$obj->favourite("food") eq "taco"
The methods will be called in the order you supply them and will be called in
scalar context. If you need to test methods called in list context then you
should use
listmethods().
NOTE Just as in a normal test script, you need to be careful if the
methods you call have side effects like changing the object or other objects
in the structure. Although the order of the methods is fixed, the order of
some other tests is not so if $expected is
{
manager => methods(@manager_methods),
coder => methods(@coder_methods)
}
there is no way to know which if manager and coder will be tested first. If the
methods you are testing depend on and alter global variables or if manager and
coder are the same object then you may run into problems.
listmethods(%hash)
%hash is a hash of method call => expected value pairs.
This is almost identical to
methods() except the methods are called in
list context instead of scalar context. This means that the expected values
supplied must be an array reference.
cmp_deeply(
$obj,
listmethods(
name => "John",
["favourites", "food"] => ["Mapo tofu", "Gongbao chicken"]
)
);
is the equivalent of checking that
$obj->name eq "John"
cmp_deeply([$obj->favourites("food")], ["Mapo tofu", "Gongbao chicken"]);
The methods will be called in the order you supply them.
NOTE The same caveats apply as for
methods().
shallow($thing)
$thing is a ref.
This prevents Test::Deep from looking inside $thing. It allows you to check that
$got_v and $thing are references to the same variable. So
my @a = @b = (1, 2, 3);
cmp_deeply(\@a, \@b);
will pass because @a and @b have the same elements however
cmp_deeply(\@a, shallow(\@b))
will fail because although \@a and \@b both contain "1, 2, 3" they are
references to different arrays.
noclass($thing)
$thing is a structure to be compared against.
This makes Test::Deep ignore the class of objects, so it just looks at the data
they contain. Class checking will be turned off until Test::Deep is finished
comparing $got_v against $thing. Once Test::Deep comes out of $thing it will
go back to it's previous setting for checking class.
This can be useful when you want to check that objects have been constructed
correctly but you don't want to write lots of "bless"es. If @people
is an array of Person objects then
cmp_deeply(\@people, noclass([
bless {name => 'John', phone => '555-5555'}, "Person",
bless {name => 'Anne', phone => '444-4444'}, "Person",
]));
can be replaced with
cmp_deeply(\@people, noclass([
{name => 'John', phone => '555-5555'},
{name => 'Anne', phone => '444-4444'}
]));
However, this is testing so you should also check that the objects are blessed
correctly. You could use a map to bless all those hashes or you could do a
second test like
cmp_deeply(\@people, array_each(isa("Person"));
useclass($thing)
This turns back on the class comparison while inside a
noclass().
cmp_deeply(
$got,
noclass(
[
useclass( $object )
]
)
)
In this example the class of the array reference in $got is ignored but the
class of $object is checked, as is the class of everything inside $object.
re($regexp, $capture_data, $flags)
$regexp is either a regular expression reference produced with
"qr/.../" or a string which will be used to construct a regular
expression.
$capture_data is optional and is used to check the strings captured by an regex.
This should can be an array ref or a Test::Deep comparator that works on array
refs.
$flags is an optional string which controls whether the regex runs as a global
match. If $flags is "g" then the regex will run as m/$regexp/g.
Without $capture_data, this simply compares $got_v with the regular expression
provided. So
cmp_deeply($got, [ re("ferg") ])
is the equivalent of
$got->[0] =~ /ferg/
With $capture_data
cmp_deeply($got, [re($regex, $capture_data)])
is the equivalent of
my @data = $got->[0] =~ /$regex/;
cmp_deeply(\@data, $capture_data);
So you can do something simple like
cmp_deeply($got, re(qr/(\d\d)(\w\w)/, [25, "ab" ]))
to check that (\d\d) was 25 and (\w\w) was "ab" but you can also use
Test::Deep objects to do more complex testing of the captured values
cmp_deeply("cat=2,dog=67,sheep=3,goat=2,dog=5",
re(qr/(\D+)=\d+,?/, set(qw( cat sheep dog )), "g"))
here, the regex will match the string and will capture the animal names and
check that they match the specified set, in this case it will fail,
complaining that "goat" is not in the set.
superhashof(\%hash)
This will check that the hash %$got is a "super-hash" of %hash. That
is that all the key and value pairs in %hash appear in %$got but %$got can
have extra ones also.
For example
cmp_deeply({a => 1, b => 2}, superhashof({a => 1}))
will pass but
cmp_deeply({a => 1, b => 2}, superhashof({a => 1, c => 3}))
will fail.
subhashof(\%hash)
This will check that the hash %$got is a "sub-hash" of %hash. That is
that all the key and value pairs in %$got also appear in %hash.
For example
cmp_deeply({a => 1}, subhashof({a => 1, b => 2}))
will pass but
cmp_deeply({a => 1, c => 3}, subhashof({a => 1, b => 2}))
will fail.
bag(@elements)
@elements is an array of elements.
This does a bag comparison, that is, it compares two arrays but ignores the
order of the elements so
cmp_deeply([1, 2, 2], bag(2, 2, 1))
will be a pass.
The object returned by
bag() has an
add() method.
my $bag = bag(1, 2, 3);
$bag->add(2, 3, 4);
will result in a bag containing 1, 2, 2, 3, 3, 4.
"NOTE" If you use certain special comparisons within a bag or set
comparison there is a danger that a test will fail when it should have passed.
It can only happen if two or more special comparisons in the bag are competing
to match elements. Consider this comparison
cmp_deeply(['furry', 'furball'], bag(re("^fur"), re("furb")))
There are two things that could happen, hopefully
"re("^fur")" is paired with "furry" and
"re("^furb")" is paired with "furb" and
everything is fine but it could happen that "re("^fur")"
is paired with "furball" and then "re("^furb")"
cannot find a match and so the test fails. Examples of other competing
comparisons are "bag(1, 2, 2)" vs "set(1, 2)" and
"methods(m1 => "v1", m2 => "v2")" vs
"methods(m1 => "v1")"
This problem is could be solved by using a slower and more complicated algorithm
for set and bag matching. Something for the future...
set(@elements)
@elements is an array of elements.
This does a set comparison, that is, it compares two arrays but ignores the
order of the elements and it ignores duplicate elements, so
cmp_deeply([1, 2, 2, 3], set(3, 2, 1, 1))
will be a pass.
The object returned by
set() has an
add() method.
my $set = set(1, 2);
$set->add(1, 3, 1);
will result in a set containing 1, 2, 3.
"NOTE" See the NOTE on the
bag() comparison for some dangers in
using special comparisons inside
set()
superbagof(@elements), subbagof(@elements), supersetof(@elements) and
subsetof(@elements)
@elements is an array of elements.
These do exactly what you'd expect them to do, so for example
cmp_deeply($data, subbagof(1, 1, 3, 4));
checks that @$data contains at most 2 "1"s, 1 "3" and 1
"4" and
cmp_deeply($data, supersetof(1, 1, 1, 4));
will check that @$data has at least one "1" and at least one
"4".
These are just special cases of the Set and Bag comparisons so they also give
you an
add() method and they also have the same limitations when using
special comparisons inside them (see the NOTE in the
bag() section).
all(@expecteds)
@expecteds is an array of expected structures.
This allows you to compare data against multiple expected results and make sure
each of them matches.
cmp_deeply($got, all(isa("Person"), methods(name => 'John')))
is equivalent to
$got->isa("Person")
$got->name eq 'John'
If either test fails then the whole thing is considered a fail. This is a
short-circuit test, the testing is stopped after the first failure, although
in the future it may complete all tests so that diagnostics can be output for
all failures. When reporting failure, the parts are counted from 1.
Thanks to the magic of overloading, you can write
any( re("^wi"), all(isa("Person"), methods(name => 'John')) )
as
re("^wi") | isa("Person") & methods(name => 'John')
Note
single | not double, as || cannot be overloaded. This will only work
when there is a special comparison involved. If you write
"john" | "anne" | "robert"
Perl will turn this into
"{onort"
which is presumably not what you wanted. This is because Perl |s them together
as strings before Test::Deep gets a chance to do any overload tricks.
any(@expecteds)
@expecteds is an array of expected structures.
This can be used to compare data against multiple expected results and make sure
that at least one of them matches. This is a short-circuit test so if a test
passes then none of the tests after that will be attempted.
You can also use overloading with | similarly to
all().
isa($class), Isa($class)
$class is a class name.
This uses
UNIVERSAL::isa() to check that $got_v is blessed into the class
$class.
NOTE: Isa() does exactly as documented here, but
isa() is
slightly different. If
isa() is called with 1 argument it falls through
to
Isa(). If
isa() called with 2 arguments, it falls through to
UNIVERSAL::isa. This is to prevent breakage when you import
isa() into
a package that is used as a class. Without this, anyone calling
"Class->isa($other_class)" would get the wrong answer. This is a
hack to patch over the fact that isa is exported by default.
array_each($thing)
$thing is a structure to be compared against.
<$got_v> must be an array reference. Each element of it will be compared
to $thing. This is useful when you have an array of similar things, for
example objects of a known type and you don't want to have to repeat the same
test for each one.
my $common_tests = all(
isa("MyFile"),
methods(
handle => isa("IO::Handle")
filename => re("^/home/ted/tmp"),
)
);
cmp_deeply($got, array_each($common_tests));
is similar to
foreach my $got_v (@$got) {
cmp_deeply($got_v, $common_tests)
}
Except it will not explode if $got is not an array reference. It will check that
each of the objects in @$got is a MyFile and that each one gives the correct
results for it's methods.
You could go further, if for example there were 3 files and you knew the size of
each one you could do this
cmp_deeply(
$got,
all(
array_each($common_tests),
[
methods(size => 1000),
methods(size => 200),
methods(size => 20)
]
)
)
cmp_deeply($got, array_each($structure));
str($string)
$string is a string.
This will stringify $got_v and compare it to $string using "eq", even
if $got_v is a ref. It is useful for checking the stringified value of an
overloaded reference.
num($number, $tolerance)
$number is a number. $tolerance is an optional number.
This will add 0 to $got_v and check if it's numerically equal to $number, even
if $got_v is a ref. It is useful for checking the numerical value of an
overloaded reference. If $tolerance is supplied then this will check that
$got_v and $exp_v are less than $tolerance apart. This is useful when
comparing floating point numbers as rounding errors can make it hard or
impossible for $got_v to be exactly equal to $exp_v. When $tolerance is
supplied, the test passes if "abs($got_v - $exp_v) <=
$tolerance".
Note in Perl, ""12blah" == 12" because Perl will be
smart and convert "12blah" into 12. You may not want this. There was
a strict mode but that is now gone. A "lookslike s number" test will
replace it soon. Until then you can usually just use the
string()
comparison to be more strict. This will work fine for almost all situations,
however it will not work when <$got_v> is an overloaded value who's
string and numerical values differ.
bool($value)
$value is anything you like but it's probably best to use 0 or 1
This will check that $got_v and $value have the same truth value, that is they
will give the same result when used in boolean context, like in an
if()
statement.
code(\&subref)
\&subref is a reference to a subroutine which will be passed a single
argument, it then should return a true or false and possibly a string
This will pass $got_v to the subroutine which returns true or false to indicate
a pass or fail. Fails can be accompanied by a diagnostic string which gives an
explanation of why it's a fail.
sub check_name
{
my $name = shift;
if ($boss->likes($name))
{
return 1;
}
else
{
return (0, "the boss doesn't like your name");
}
}
cmp_deeply("Brian", code(\&check_name));
DIAGNOSTIC FUNCTIONS¶
my $reason = deep_diag($stack)
$stack is a value returned by cmp_details. Do not call this function if
cmp_details returned a true value for $ok.
deep_diag() returns a human readable string describing how the comparison
failed.
ANOTHER EXAMPLE¶
You've written a module to handle people and their film interests. Say you have
a function that returns an array of people from a query, each person is a hash
with 2 keys: Name and Age and the array is sorted by Name. You can do
cmp_deeply(
$result,
[
{Name => 'Anne', Age => 26},
{Name => "Bill", Age => 47}
{Name => 'John', Age => 25},
]
);
Soon after, your query function changes and all the results now have an ID
field. Now your test is failing again because you left out ID from each of the
hashes. The problem is that the IDs are generated by the database and you have
no way of knowing what each person's ID is. With Test::Deep you can change
your query to
cmp_deeply(
$result,
[
{Name => 'John', Age => 25, ID => ignore()},
{Name => 'Anne', Age => 26, ID => ignore()},
{Name => "Bill", Age => 47, ID => ignore()}
]
);
But your test still fails. Now, because you're using a database, you no longer
know what order the people will appear in. You could add a sort into the
database query but that could slow down your application. Instead you can get
Test::Deep to ignore the order of the array by doing a bag comparison instead.
cmp_deeply(
$result,
bag(
{Name => 'John', Age => 25, ID => ignore()},
{Name => 'Anne', Age => 26, ID => ignore()},
{Name => "Bill", Age => 47, ID => ignore()}
)
);
Finally person gets even more complicated and includes a new field called
Movies, this is a list of movies that the person has seen recently, again
these movies could also come back in any order so we need a bag inside our
other bag comparison, giving us something like
cmp_deeply(
$result,
bag(
{Name => 'John', Age => 25, ID => ignore(), Movies => bag(...)},
{Name => 'Anne', Age => 26, ID => ignore(), Movies => bag(...)},
{Name => "Bill", Age => 47, ID => ignore(), Movies => bag(...)}
)
);
USING TEST::DEEP WITH TEST::BUILDER¶
Combining "cmp_details" and "test_diag" makes it possible to
use Test::Deep in your own test classes.
In a Test::Builder subclass, create a test method in the following form:
sub behaves_ok {
my $self = shift;
my $expected = shift;
my $test_name = shift;
my $got = do_the_important_work_here();
my ($ok, $stack) = cmp_details($got, $expected);
unless ($Test->ok($ok, $test_name)) {
my $diag = deep_diag($stack);
$Test->diag($diag);
}
}
As the subclass defines a test class, not tests themselves, make sure it uses
Test::Deep::NoTest, not "Test::Deep" itself.
LIMITATIONS¶
Currently any CODE, GLOB or IO refs will be compared using
shallow(),
which means only their memory addresses are compared.
BUGS¶
There is a bug in set and bag compare to do with competing SCs. It only occurs
when you put certain special comparisons inside bag or set comparisons you
don't need to worry about it. The full details are in the
bag() docs.
It will be fixed in an upcoming version.
WHAT ARE SPECIAL COMPARISONS?¶
A special comparison (SC) is simply an object that inherits from
Test::Deep::Cmp. Whenever $expected_v is an SC then instead of checking
"$got_v eq $expected_v", we pass control over to the SC and let it
do it's thing.
Test::Deep exports lots of SC constructors, to make it easy for you to use them
in your test scripts. For example is "re("hello")" is just
a handy way of creating a Test::Deep::Regexp object that will match any string
containing "hello". So
cmp_deeply([ 'a', 'b', 'hello world'], ['a', 'b', re("^hello")]);
will check 'a' eq 'a', 'b' eq 'b' but when it comes to comparing 'hello world'
and "re("^hello")" it will see that $expected_v is an SC
and so will pass control to the Test::Deep::Regexp class by do something like
"$expected_v->descend($got_v)". The "descend()" method
should just return true or false.
This gives you enough to write your own SCs but I haven't documented how
diagnostics works because it's about to get an overhaul.
SEE ALSO¶
Test::More
MAINTAINER¶
Ricardo Signes <rjbs@cpan.org>
AUTHOR¶
Fergal Daly <fergal@esatclear.ie>, with thanks to Michael G Schwern for
Test::More's is_deeply function which inspired this.
Please do not bother Fergal Daly with bug reports. Send them to the
maintainer (above) or submit them at the request tracker
<
https://rt.cpan.org/Dist/Display.html?Queue=Test-Deep>.
COPYRIGHT¶
Copyright 2003, 2004 by Fergal Daly <fergal@esatclear.ie>.
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
See
http://www.perl.com/perl/misc/Artistic.html