2019 twenty-four merry days of Perl Feed

Test2: Test Harder (but easier)

Test2::V0 - 2019-12-21

"Right, my fellow Elves, calm down", the Wise Old Elf shouted over the rabble gathed in the elf lecture hall, "Today I'm going to be talking to you about Testing"

There were loud groans from the audience. They'd been writing tests for years. It was like teaching their Grandmother to suck Eggnog.

"Now now...how many of you are familiar with the latest changes in Test2?"

Less noise now. Maybe there was something here they could learn after all.

"There's so much to cover. I could tell you about the underlying event system that allows decoupling of parts of the test system. I could talk about the new structure of creating interoperable test frameworks. I could talk to about the new harness features...but today, today I'm going to talk to you about Test2::V0.

Test2::V0 is like a smorgasbord of all the good bits of Test2 wrapped up in one delectable package. When you might previously grab Test::More, you should grab Test2::V0. Because...because it not only uses all of the cool tech on its backend, but because it's so darn handy to use."

Making the Easy Stuff Easy: Strictness, Warnings and UTF8

"Lazyness! One of the greatest virtue of the Perl programmer! Why type a lot when you can type a little? Why not have sensible defaults."

There were plenty of nodding heads now. Writing tests is a Cost of Doing Business - so making it as simple as possible to do the right thing without thinking about it is critical.

The Wise Old Elf threw the most basic Perl script up on the screen.


use strict;
use warnings;

use Test::More tests => 1;

ok(1, 'Do we want to build a \N{SNOWMAN}?');

"Now here's the same code written in an idiomatic fashion with Test2::V0."


use Test2::V0;

ok(1, "Do you want to build a \N{SNOWMAN}?");


"Who can spot the difference?"

Tiramisu Shinytree raised her hand. "There's no strict or warnings!"

"Correct! Test2::V0 (like Moose, Mojolicious, and many other common tools) turns those on for you automatically. Anything else?"

It was Bluebell Brandycake's turn. "There's no plan!"

"Well yes, Test2 allows you to use done_testing rather than having to count each and every test and declare a plan, but modern versions of Test::More allow that too. Anything else? Anyone spot the bug?"

Silence. Can you spot it? The Wise Old Elf decided to show the class the output of the scripts.

    shell $ perl /tmp/more.t
    Wide character in print at /opt/perl/bin/lib/site_perl/5.28.1/Test2/Formatter/TAP.pm line 144.
    ok 1 - Do you want to build a X?

    shell $ perl /tmp/2v0.t
    ok 1 - Do you want to build a X?

The crowd groaned. They'd forgotten Fowler's Rule on Unicode (there's always another unicode bug, you just haven't found it yet)

"Yep. Test2::V0 also reconfigures the output handles to encode as UTF-8 which I bet you always forget - until you see that warning message."

Deep Testing

"The next thing you'll notice is that Test2::V0 based tests are, well, naturally deeper than their Test::More counterparts. Where in Test::More if you wanted to test data structures you'd have to use is_deeply..."


use strict;
use warnings;

use Test::More tests => 1;

use Reindeer::Santa qw(original_team);
my @results = original_team();

is_deeply(\@original_tam, [
    'Dasher', 'Dancer', 'Prancer', 'Vixen',
    'Comet', 'Cupid', 'Donner', 'Blitzen',
], 'check reindeer');

"With Test2::V0 you'd just use is."


use Test2::V0

use Reindeer::Santa qw(original_team);
my @results = original_team();

is(\@original_tam, [
    'Dasher', 'Dancer', 'Prancer', 'Vixen',
    'Comet', 'Cupid', 'Donner', 'Blitzen',
], 'check reindeer');

The Wise Old Elf went onto explain it was so much more. To demonstrate, he set a little programming exercise.

Write a test that checks the output is a hashref that has three entries in it. The first is a name (which must be a string). The second is an age which must be equal to eighteen or the string "adult". The third is an info array that has four elements: A true value, an instance of Snowman, an instance that has an as_string method that returns Anna, and finally something that is a valid RFC 1123 date time. The top level hash can have any other alphanumeric keys except error.

The elves spent a long time producing page after page of code. There were debates. Arguments. And thirty minutes later no-one was done.

They were quite shocked when the Wise Old elf showed them his simple solution:

is($data, hash {
# insist that name is a string (not a ref, etc!)
field name => match qr//;

# insist that the person's age 18 (or 18.0, etc) or "adult"
field age => in_set(number(18), "adult");

# info is an array
field info => array {
# the first element must be a true value
item T();

# the second element must be an instance of Snowman
item object { blessed => 'Snowman' };

# the third element must return 'Anna' when as_string is called on it
item object { call as_string => 'Anna' };

# the fourth element must be parseable as a RFC 1123 time
       # the validator sub must return true if passes, false if not
       # (and Try::Tiny's try returns undef on exception)
item validator(sub {
           return try {
               DateTime::Format::HTTP->parse_datetime( $_ );

# and there must only be four elements

# we don't want a field called "error"
field error => DNE(); # does not exist

# allow any other fields that keys are alphanumeric
all_keys(match qr/^[A-Za-z0-9]+$/aa);
   }, "compare");

Exception Checking

"Sparkle Candytoes, what are an elf's favorite colors?"

Sparkle beamed. "Red and Green, Wise Old Elf"

"Correct! When we write good tests we don't just test the green path - what our code does wh its supposed to, we also check the red path. Does it handle hte errors correctly".

"We want to make sure that our code throws the right exceptions. Without the exception breaking our test of course! Test2::V0 has its own exception capturing code:"

 use autodie;

ok(dies {
    open my $fh, "<", "file-that-does-not-exist";
}, 'open throws exception on non existent file');

"Since dies returns the actual exception thrown we can improve the test, by checking if the exception contained the right string:

    like(dies {
       open my $fh, "<", "file-that-does-not-exist";
    }, qr/No such file/, 'open throws exception on non existent file');

Or even check that something dies with the right kind of errors

    isa_ok(dies {
    }, 'Mojo::Exception', 'exception was an instance of Mojo::Exception);


"Now class, who can spot the problem with this code?"

use Test::More;

subtest 'horse' => sub {
    is $cart, 'cart', 'cart';


No hands up. "Cinnamon Candybubbles, how about you".

"I think it works, Wise Old Elf"

"Oh, it does, it does. It just looks confusing"

    # Subtest: horse
        not ok 1 - cart
        #   Failed test 'cart'
        #   at - line 4.
        #          got: undef
        #     expected: 'cart'
        # Looks like you failed 1 test of 1.
    not ok 1 - horse
    #   Failed test 'horse'
    #   at - line 5.

"You have to read the comments to figure out what's going on. The cart is literally before the horse."

The Wise Old Elf showed them the same code in Test2::V0:

use Test2::V0;  # only this line changed!

subtest 'horse' => sub {
    is $cart, 'cart', 'cart';


But the output is very different

    not ok 1 - horse {
        not ok 1 - cart
        # Failed test 'cart'
        # at - line 5.
        # +---------+-------+
        # | GOT     | CHECK |
        # +---------+-------+
        # | <UNDEF> | cart  |
        # +---------+-------+
    # Failed test 'horse'
    # at - line 6.

And More

"Now class, I'd like to talk to you about...", began the Wise Old Elf, only to be interrupted by the ringing of the lunch bell. Test2 is a big topic. More will have to wait for another day...

Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>