Perl Testing

# Step 1: RED — Write a failing test# t/unit/calculator.tuse 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($calc->add(-1, 1), 0, 'handles negatives');};
done_testing;
# Step 2: GREEN — Write minimal implementation# lib/Calculator.pmpackage Calculator;use v5.36;use Moo;
sub add($self, $a, $b) {    return $a + $b;}
1;
# Step 3: REFACTOR — Improve while tests stay green# Run: prove -lv t/unit/calculator.t

use v5.36;use Test::More;
# Plan upfront or use done_testing# plan tests => 5;  # Fixed plan (optional)
# Equalityis($result, 42, 'returns correct value');isnt($result, 0, 'not zero');
# Booleanok($user->is_active, 'user is active');ok(!$user->is_banned, 'user is not banned');
# Deep comparisonis_deeply(    $got,    { name => 'Alice', roles => ['admin'] },    'returns expected structure');
# Pattern matchinglike($error, qr/not found/i, 'error mentions not found');unlike($output, qr/password/, 'output hides password');
# Type checkisa_ok($obj, 'MyApp::User');can_ok($obj, 'save', 'delete');
done_testing;

use v5.36;use Test::More;
# Skip tests conditionallySKIP: {    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 failuresTODO: {    local $TODO = 'Caching not yet implemented';    is($cache->get('key'), 'value', 'cache returns value');}
done_testing;

use v5.36;use Test2::V0;
# Hash builder — check partial structureis(    $user->to_hash,    hash {        field name  => 'Alice';        field email => match(qr/\@example\.com$/);        field age   => validator(sub { $_ >= 18 });        # Ignore other fields        etc();    },    'user has expected fields');
# Array builderis(    $result,    array {        item 'first';        item match(qr/^second/);        item DNE();  # Does Not Exist — verify no extra items    },    'result matches expected list');
# Bag — order-independent comparisonis(    $tags,    bag {        item 'perl';        item 'testing';        item 'tdd';    },    'has all required tags regardless of order');

use v5.36;use Test2::V0;
subtest 'User creation' => sub {    my $user = User->new(name => 'Alice', email => '[email protected]');    ok($user, 'user object created');    is($user->name, 'Alice', 'name is set');    is($user->email, '[email protected]', 'email is set');};
subtest 'User validation' => sub {    my $warnings = warns {        User->new(name => '', email => 'bad');    };    ok($warnings, 'warns on invalid data');};
done_testing;

use v5.36;use Test2::V0;
# Test that code dieslike(    dies { divide(10, 0) },    qr/Division by zero/,    'dies on division by zero');
# Test that code livesok(lives { divide(10, 2) }, 'division succeeds') or note($@);
# Combined patternsubtest '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;

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)};

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 => '[email protected]' };    });
    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

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;

# Bad: Test file runs but doesn't verify all tests executeduse Test2::V0;is(1, 1, 'works');# Missing done_testing — silent bugs if test code is skipped
# Good: Always end with done_testinguse Test2::V0;is(1, 1, 'works');done_testing;