feat: add Perl skills (patterns, security, testing)

skills/perl-testing/SKILL.md

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+---
+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.
+
+```perl
+# 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 + $b;
+}
+
+1;
+
+# Step 3: REFACTOR — Improve while tests stay green
+# Run: prove -lv t/unit/calculator.t
+```
+
+## Test::More Fundamentals
+
+The standard Perl testing module — widely used, ships with core.
+
+### Basic Assertions
+
+```perl
+use v5.36;
+use Test::More;
+
+# Plan upfront or use done_testing
+# plan tests => 5;  # Fixed plan (optional)
+
+# Equality
+is($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
+
+```perl
+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
+
+```perl
+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
+
+```perl
+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
+
+```perl
+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
+
+```text
+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        # Test data files
+    └── users.csv
+```
+
+### prove Commands
+
+```bash
+# Run all tests
+prove -l t/
+
+# Verbose output
+prove -lv t/
+
+# Run specific test
+prove -lv t/unit/user.t
+
+# Recursive search
+prove -lr t/
+
+# Parallel execution (8 jobs)
+prove -lr -j8 t/
+
+# Run only failing tests from last run
+prove -l --state=failed t/
+
+# Colored output with timer
+prove -l --color --timer t/
+
+# TAP output for CI
+prove -l --formatter TAP::Formatter::JUnit t/ > results.xml
+```
+
+### .proverc Configuration
+
+```text
+-l
+--color
+--timer
+-r
+-j4
+--state=save
+```
+
+## Fixtures and Setup/Teardown
+
+### Subtest Isolation
+
+```perl
+use v5.36;
+use Test2::V0;
+use File::Temp qw(tempdir);
+use Path::Tiny;
+
+subtest 'file processing' => sub {
+    # Setup
+    my $dir = tempdir(CLEANUP => 1);
+    my $file = path($dir, 'input.txt');
+    $file->spew_utf8("line1\nline2\nline3\n");
+
+    # Test
+    my $result = process_file("$file");
+    is($result->{line_count}, 3, 'counts lines');
+
+    # Teardown happens automatically (CLEANUP => 1)
+};
+```
+
+### Shared Test Helpers
+
+Place reusable helpers in `t/lib/TestHelper.pm` and load with `use lib 't/lib'`. Export factory functions like `create_test_db()`, `create_temp_dir()`, and `fixture_path()` via `Exporter`.
+
+## Mocking
+
+### Test::MockModule
+
+```perl
+use v5.36;
+use Test2::V0;
+use Test::MockModule;
+
+subtest 'mock external API' => sub {
+    my $mock = Test::MockModule->new('MyApp::API');
+
+    # Good: Mock returns controlled data
+    $mock->mock(fetch_user => sub ($self, $id) {
+        return { id => $id, name => 'Mock User', email => 'mock@test.com' };
+    });
+
+    my $api = MyApp::API->new;
+    my $user = $api->fetch_user(42);
+    is($user->{name}, 'Mock User', 'returns mocked user');
+
+    # Verify call count
+    my $call_count = 0;
+    $mock->mock(fetch_user => sub { $call_count++; return {} });
+    $api->fetch_user(1);
+    $api->fetch_user(2);
+    is($call_count, 2, 'fetch_user called twice');
+
+    # Mock is automatically restored when $mock goes out of scope
+};
+
+# Bad: Monkey-patching without restoration
+# *MyApp::API::fetch_user = sub { ... };  # NEVER — leaks across tests
+```
+
+For lightweight mock objects, use `Test::MockObject` to create injectable test doubles with `->mock()` and verify calls with `->called_ok()`.
+
+## Coverage with Devel::Cover
+
+### Running Coverage
+
+```bash
+# Basic coverage report
+cover -test
+
+# Or step by step
+perl -MDevel::Cover -Ilib t/unit/user.t
+cover
+
+# HTML report
+cover -report html
+open cover_db/coverage.html
+
+# Specific thresholds
+cover -test -report text | grep 'Total'
+
+# CI-friendly: fail under threshold
+cover -test && cover -report text -select '^lib/' \
+  | perl -ne 'if (/Total.*?(\d+\.\d+)/) { exit 1 if $1 < 80 }'
+```
+
+### Integration Testing
+
+Use in-memory SQLite for database tests, mock HTTP::Tiny for API tests.
+
+```perl
+use v5.36;
+use Test2::V0;
+use DBI;
+
+subtest 'database integration' => sub {
+    my $dbh = DBI->connect('dbi:SQLite:dbname=:memory:', '', '', {
+        RaiseError => 1,
+    });
+    $dbh->do('CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)');
+
+    $dbh->prepare('INSERT INTO users (name) VALUES (?)')->execute('Alice');
+    my $row = $dbh->selectrow_hashref('SELECT * FROM users WHERE name = ?', undef, 'Alice');
+    is($row->{name}, 'Alice', 'inserted and retrieved user');
+};
+
+done_testing;
+```
+
+## Best Practices
+
+### DO
+
+- **Follow TDD**: Write tests before implementation (red-green-refactor)
+- **Use Test2::V0**: Modern assertions, better diagnostics
+- **Use subtests**: Group related assertions, isolate state
+- **Mock external dependencies**: Network, database, file system
+- **Use `prove -l`**: Always include lib/ in `@INC`
+- **Name tests clearly**: `'user login with invalid password fails'`
+- **Test edge cases**: Empty strings, undef, zero, boundary values
+- **Aim for 80%+ coverage**: Focus on business logic paths
+- **Keep tests fast**: Mock I/O, use in-memory databases
+
+### DON'T
+
+- **Don't test implementation**: Test behavior and output, not internals
+- **Don't share state between subtests**: Each subtest should be independent
+- **Don't skip `done_testing`**: Ensures all planned tests ran
+- **Don't over-mock**: Mock boundaries only, not the code under test
+- **Don't use `Test::More` for new projects**: Prefer Test2::V0
+- **Don't ignore test failures**: All tests must pass before merge
+- **Don't test CPAN modules**: Trust libraries to work correctly
+- **Don't write brittle tests**: Avoid over-specific string matching
+
+## Quick Reference
+
+| Task | Command / Pattern |
+|---|---|
+| Run all tests | `prove -lr t/` |
+| Run one test verbose | `prove -lv t/unit/user.t` |
+| Parallel test run | `prove -lr -j8 t/` |
+| Coverage report | `cover -test && cover -report html` |
+| Test equality | `is($got, $expected, 'label')` |
+| Deep comparison | `is($got, hash { field k => 'v'; etc() }, 'label')` |
+| Test exception | `like(dies { ... }, qr/msg/, 'label')` |
+| Test no exception | `ok(lives { ... }, 'label')` |
+| Mock a method | `Test::MockModule->new('Pkg')->mock(m => sub { ... })` |
+| Skip tests | `SKIP: { skip 'reason', $count unless $cond; ... }` |
+| TODO tests | `TODO: { local $TODO = 'reason'; ... }` |
+
+## Common Pitfalls
+
+### Forgetting `done_testing`
+
+```perl
+# Bad: Test file runs but doesn't verify all tests executed
+use Test2::V0;
+is(1, 1, 'works');
+# Missing done_testing — silent bugs if test code is skipped
+
+# Good: Always end with done_testing
+use Test2::V0;
+is(1, 1, 'works');
+done_testing;
+```
+
+### Missing `-l` Flag
+
+```bash
+# Bad: Modules in lib/ not found
+prove t/unit/user.t
+# Can't locate MyApp/User.pm in @INC
+
+# Good: Include lib/ in @INC
+prove -l t/unit/user.t
+```
+
+### Over-Mocking
+
+Mock the *dependency*, not the code under test. If your test only verifies that a mock returns what you told it to, it tests nothing.
+
+### Test Pollution
+
+Use `my` variables inside subtests — never `our` — to prevent state leaking between tests.
+
+**Remember**: Tests are your safety net. Keep them fast, focused, and independent. Use Test2::V0 for new projects, prove for running, and Devel::Cover for accountability.