
About
Perl testing patterns using Test2::V0, Test::More, prove runner, mocking, coverage with Devel::Cover, and TDD methodology.
name: perl-testing description: Perl testing patterns using Test2::V0, Test::More, prove runner, mocking, coverage with Devel::Cover, and TDD methodology. origin: ECC
Perl Testing Patterns
Comprehensive testing strategies for Perl applications using Test2::V0, Test::More, prove, and TDD methodology.
When to Activate
- Writing new Perl code (follow TDD: red, green, refactor)
- Designing test suites for Perl modules or applications
- Reviewing Perl test coverage
- Setting up Perl testing infrastructure
- Migrating tests from Test::More to Test2::V0
- Debugging failing Perl tests
TDD Workflow
Always follow the RED-GREEN-REFACTOR cycle.
# Step 1: RED — Write a failing test
# t/unit/calculator.t
use v5.36;
use Test2::V0;
use lib 'lib';
use Calculator;
subtest 'addition' => sub {
my $calc = Calculator->new;
is($calc->add(2, 3), 5, 'adds two numbers');
is($calc->add(-1, 1), 0, 'handles negatives');
};
done_testing;
# Step 2: GREEN — Write minimal implementation
# lib/Calculator.pm
package Calculator;
use v5.36;
use Moo;
sub add($self, $a, $b) {
return $a + $b;
}
1;
# Step 3: REFACTOR — Improve while tests stay green
# Run: prove -lv t/unit/calculator.t
Test::More Fundamentals
The standard Perl testing module — widely used, ships with core.
Basic Assertions
use v5.36;
use Test::More;
# Plan upfront or use done_testing
# plan tests => 5; # Fixed plan (optional)
# Equality
is($result, 42, 'returns correct value');
isnt($result, 0, 'not zero');
# Boolean
ok($user->is_active, 'user is active');
ok(!$user->is_banned, 'user is not banned');
# Deep comparison
is_deeply(
$got,
{ name => 'Alice', roles => ['admin'] },
'returns expected structure'
);
# Pattern matching
like($error, qr/not found/i, 'error mentions not found');
unlike($output, qr/password/, 'output hides password');
# Type check
isa_ok($obj, 'MyApp::User');
can_ok($obj, 'save', 'delete');
done_testing;
SKIP and TODO
use v5.36;
use Test::More;
# Skip tests conditionally
SKIP: {
skip 'No database configured', 2 unless $ENV{TEST_DB};
my $db = connect_db();
ok($db->ping, 'database is reachable');
is($db->version, '15', 'correct PostgreSQL version');
}
# Mark expected failures
TODO: {
local $TODO = 'Caching not yet implemented';
is($cache->get('key'), 'value', 'cache returns value');
}
done_testing;
Test2::V0 Modern Framework
Test2::V0 is the modern replacement for Test::More — richer assertions, better diagnostics, and extensible.
Why Test2?
- Superior deep comparison with hash/array builders
- Better diagnostic output on failures
- Subtests with cleaner scoping
- Extensible via Test2::Tools::* plugins
- Backward-compatible with Test::More tests
Deep Comparison with Builders
use v5.36;
use Test2::V0;
# Hash builder — check partial structure
is(
$user->to_hash,
hash {
field name => 'Alice';
field email => match(qr/\@example\.com$/);
field age => validator(sub { $_ >= 18 });
# Ignore other fields
etc();
},
'user has expected fields'
);
# Array builder
is(
$result,
array {
item 'first';
item match(qr/^second/);
item DNE(); # Does Not Exist — verify no extra items
},
'result matches expected list'
);
# Bag — order-independent comparison
is(
$tags,
bag {
item 'perl';
item 'testing';
item 'tdd';
},
'has all required tags regardless of order'
);
Subtests
use v5.36;
use Test2::V0;
subtest 'User creation' => sub {
my $user = User->new(name => 'Alice', email => 'alice@example.com');
ok($user, 'user object created');
is($user->name, 'Alice', 'name is set');
is($user->email, 'alice@example.com', 'email is set');
};
subtest 'User validation' => sub {
my $warnings = warns {
User->new(name => '', email => 'bad');
};
ok($warnings, 'warns on invalid data');
};
done_testing;
Exception Testing with Test2
use v5.36;
use Test2::V0;
# Test that code dies
like(
dies { divide(10, 0) },
qr/Division by zero/,
'dies on division by zero'
);
# Test that code lives
ok(lives { divide(10, 2) }, 'division succeeds') or note($@);
# Combined pattern
subtest 'error handling' => sub {
ok(lives { parse_config('valid.json') }, 'valid config parses');
like(
dies { parse_config('missing.json') },
qr/Cannot open/,
'missing file dies with message'
);
};
done_testing;
Test Organization and prove
Directory Structure
t/
├── 00-load.t # Verify modules compile
├── 01-basic.t # Core functionality
├── unit/
│ ├── config.t # Unit tests by module
│ ├── user.t
│ └── util.t
├── integration/
│ ├── database.t
│ └── api.t
├── lib/
│ └── TestHelper.pm # Shared test utilities
└── fixtures/
├── config.json
Compatible Tools
Claude CodeCursor
Tags
Testing

