Test Driven Development

Test-Driven Development (TDD) for Laravel

Overview

Write the test first. Watch it fail. Write minimal code to pass.

Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.

Violating the letter of the rules is violating the spirit of the rules.

When to Use

Always:

• New features
• Bug fixes
• Refactoring
• Behavior changes

Exceptions (ask your human partner):

• Throwaway prototypes
• Generated code (migrations, factories)
• Configuration files

Thinking "skip TDD just this once"? Stop. That's rationalization.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

No exceptions:

• Don't keep it as "reference"
• Don't "adapt" it while writing tests
• Don't look at it
• Delete means delete

Implement fresh from tests. Period.

Red-Green-Refactor

RED - Write Failing Test

Write one minimal test showing what should happen.

Good:

test('retries failed operations 3 times', function () {
    $attempts = 0;

    $operation = function () use (&$attempts) {
        $attempts++;
        if ($attempts < 3) {
            throw new Exception('fail');
        }
        return 'success';
    };

    $result = retryOperation($operation);

    expect($result)->toBe('success');
    expect($attempts)->toBe(3);
});

Clear name, tests real behavior, one thing

Bad:

test('retry works', function () {
    $mock = Mockery::mock(SomeService::class);
    $mock->shouldReceive('call')
        ->times(3)
        ->andThrow(new Exception(), new Exception())
        ->andReturn('success');

    retryOperation(fn () => $mock->call());

    // Only verifies mock was called, not actual behavior
});

Vague name, tests mock not code

Requirements:

• One behavior
• Clear name
• Real code (no mocks unless unavoidable)

Verify RED - Watch It Fail

MANDATORY. Never skip.

php artisan test --filter="retries failed operations"

Confirm:

• Test fails (not errors)
• Failure message is expected
• Fails because feature missing (not typos)

Test passes? You're testing existing behavior. Fix test.

Test errors? Fix error, re-run until it fails correctly.

GREEN - Minimal Code

Write simplest code to pass the test.

Good:

function retryOperation(callable $fn, int $maxRetries = 3): mixed
{
    for ($i = 0; $i < $maxRetries; $i++) {
        try {
            return $fn();
        } catch (Exception $e) {
            if ($i === $maxRetries - 1) {
                throw $e;
            }
        }
    }
}

Just enough to pass

Bad:

function retryOperation(
    callable $fn,
    int $maxRetries = 3,
    string $backoff = 'exponential',
    ?callable $onRetry = null,
    ?LoggerInterface $logger = null,
): mixed {
    // YAGNI - You Aren't Gonna Need It
}

Over-engineered

Don't add features, refactor other code, or "improve" beyond the test.

Verify GREEN - Watch It Pass

MANDATORY.

php artisan test --filter="retries failed operations"

Confirm:

• Test passes
• Other tests still pass
• Output pristine (no errors, warnings, deprecations)

Test fails? Fix code, not test.

Other tests fail? Fix now.

REFACTOR - Clean Up

After green only:

• Remove duplication
• Improve names
• Extract to Actions, Services, or helpers

Keep tests green. Don't add behavior.

Repeat

Next failing test for next feature.

Good Tests

Why Order Matters

"I'll write tests after to verify it works"

Tests written after code pass immediately. Passing immediately proves nothing:

• Might test wrong thing
• Might test implementation, not behavior
• Might miss edge cases you forgot
• You never saw it catch the bug

Test-first forces you to see the test fail, proving it actually tests something.

"I already manually tested all the edge cases"

Manual testing is ad-hoc. You think you tested everything but:

• No record of what you tested
• Can't re-run when code changes
• Easy to forget cases under pressure
• "It worked when I tried it" ≠ comprehensive

Automated tests are systematic. They run the same way every time.

"Deleting X hours of work is wasteful"

Sunk cost fallacy. The time is already gone. Your choice now:

• Delete and rewrite with TDD (X more hours, high confidence)
• Keep it and add tests after (30 min, low confidence, likely bugs)

The "waste" is keeping code you can't trust. Working code without real tests is technical debt.

"TDD is dogmatic, being pragmatic means adapting"

TDD IS pragmatic:

• Finds bugs before commit (faster than debugging after)
• Prevents regressions (tests catch breaks immediately)
• Documents behavior (tests show how to use code)
• Enables refactoring (change freely, tests catch breaks)

"Pragmatic" shortcuts = debugging in production = slower.

"Tests after achieve the same goals - it's spirit not ritual"

No. Tests-after answer "What does this do?" Tests-first answer "What should this do?"

Tests-after are biased by your implementation. You test what you built, not what's required. You verify remembered edge cases, not discovered ones.

Tests-first force edge case discovery before implementing. Tests-after verify you remembered everything (you didn't).

30 minutes of tests after ≠ TDD. You get coverage, lose proof tests work.

Common Rationalizations

Red Flags - STOP and Start Over

• Code before test
• Test after implementation
• Test passes immediately
• Can't explain why test failed
• Tests added "later"
• Rationalizing "just this once"
• "I already manually tested it"
• "Tests after achieve the same purpose"
• "It's about spirit not ritual"
• "Keep as reference" or "adapt existing code"
• "Already spent X hours, deleting is wasteful"
• "TDD is dogmatic, I'm being pragmatic"
• "This is different because..."

All of these mean: Delete code. Start over with TDD.

Laravel-Specific Examples

Example: Bug Fix with Form Request

Bug: Empty email accepted

RED

test('rejects empty email', function () {
    $response = $this->postJson('/api/users', [
        'email' => '',
        'name' => 'Test User',
    ]);

    $response->assertStatus(422)
        ->assertJsonValidationErrors(['email']);
});

Verify RED

$ php artisan test --filter="rejects empty email"
FAIL: Expected status 422, got 200

GREEN

// app/Http/Requests/StoreUserRequest.php
class StoreUserRequest extends FormRequest
{
    public function rules(): array
    {
        return [
            'email' => ['required', 'email'],
            'name' => ['required', 'string'],
        ];
    }
}

Verify GREEN

$ php artisan test --filter="rejects empty email"
PASS

Example: Action Class

RED

test('calculate order total includes tax', function () {
    $order = Order::factory()->create([
        'subtotal' => 10000, // $100.00 in cents
    ]);

    $action = new CalculateOrderTotalAction();
    $result = $action->execute($order, taxRate: 0.08);

    expect($result->total)->toBe(10800);
    expect($result->tax)->toBe(800);
});

Verify RED

$ php artisan test --filter="calculate order total"
FAIL: Class CalculateOrderTotalAction not found

GREEN

// app/Actions/CalculateOrderTotalAction.php
class CalculateOrderTotalAction
{
    public function execute(Order $order, float $taxRate): OrderTotal
    {
        $tax = (int) round($order->subtotal * $taxRate);

        return new OrderTotal(
            subtotal: $order->subtotal,
            tax: $tax,
            total: $order->subtotal + $tax,
        );
    }
}

Verify GREEN

$ php artisan test --filter="calculate order total"
PASS

Example: Policy/Gate Authorization

RED

test('users can only view their own orders', function () {
    $user = User::factory()->create();
    $otherUser = User::factory()->create();
    $order = Order::factory()->for($otherUser)->create();

    $this->actingAs($user);

    expect($user->can('view', $order))->toBeFalse();
});

test('users can view their own orders', function () {
    $user = User::factory()->create();
    $order = Order::factory()->for($user)->create();

    $this->actingAs($user);

    expect($user->can('view', $order))->toBeTrue();
});

GREEN

// app/Policies/OrderPolicy.php
class OrderPolicy
{
    public function view(User $user, Order $order): bool
    {
        return $user->id === $order->user_id;
    }
}

Example: Eloquent Scope

RED

test('active scope returns only active users', function () {
    User::factory()->count(3)->create(['active' => true]);
    User::factory()->count(2)->create(['active' => false]);

    $activeUsers = User::active()->get();

    expect($activeUsers)->toHaveCount(3);
    expect($activeUsers->pluck('active')->unique()->all())->toBe([true]);
});

GREEN

// app/Models/User.php
public function scopeActive(Builder $query): Builder
{
    return $query->where('active', true);
}

Example: Job/Queue

RED

use Illuminate\Support\Facades\Queue;

test('order completion dispatches notification job', function () {
    Queue::fake();

    $order = Order::factory()->create();
    $action = new CompleteOrderAction();

    $action->execute($order);

    Queue::assertPushed(SendOrderCompletionNotification::class, function ($job) use ($order) {
        return $job->order->id === $order->id;
    });
});

GREEN

class CompleteOrderAction
{
    public function execute(Order $order): void
    {
        $order->update(['status' => 'completed']);

        SendOrderCompletionNotification::dispatch($order);
    }
}

Example: Event Listener

RED

use Illuminate\Support\Facades\Event;

test('user registration fires UserRegistered event', function () {
    Event::fake([UserRegistered::class]);

    $action = new RegisterUserAction();
    $user = $action->execute([
        'email' => 'test@example.com',
        'password' => 'password',
    ]);

    Event::assertDispatched(UserRegistered::class, function ($event) use ($user) {
        return $event->user->id === $user->id;
    });
});

GREEN

class RegisterUserAction
{
    public function execute(array $data): User
    {
        $user = User::create([
            'email' => $data['email'],
            'password' => Hash::make($data['password']),
        ]);

        event(new UserRegistered($user));

        return $user;
    }
}

Pest-Specific Features

Use describe for Grouping Related Tests

describe('OrderPolicy', function () {
    test('owners can view their orders', function () {
        // ...
    });

    test('owners can cancel pending orders', function () {
        // ...
    });

    test('owners cannot cancel shipped orders', function () {
        // ...
    });
});

Use beforeEach for Common Setup

beforeEach(function () {
    $this->user = User::factory()->create();
    $this->actingAs($this->user);
});

test('can create order', function () {
    // $this->user is available
});

Use Datasets for Parameterized Tests

dataset('invalid_emails', [
    'empty string' => [''],
    'missing @' => ['invalidemail.com'],
    'missing domain' => ['test@'],
    'spaces' => ['test @example.com'],
]);

test('rejects invalid email formats', function (string $email) {
    $response = $this->postJson('/api/users', [
        'email' => $email,
        'name' => 'Test',
    ]);

    $response->assertJsonValidationErrors(['email']);
})->with('invalid_emails');

Use Higher-Order Tests for Simple Cases

test('homepage loads successfully')
    ->get('/')
    ->assertOk();

test('guests cannot access dashboard')
    ->get('/dashboard')
    ->assertRedirect('/login');

Verification Checklist

Before marking work complete:

• Every new Action/Service/Model method has a test
• Watched each test fail before implementing
• Each test failed for expected reason (feature missing, not typo)
• Wrote minimal code to pass each test
• All tests pass: php artisan test
• Output pristine (no errors, warnings, deprecations)
• Tests use real code (fakes only for external services)
• Edge cases and errors covered

Can't check all boxes? You skipped TDD. Start over.

Useful Commands

# Run all tests
php artisan test

# Run specific test by name
php artisan test --filter="rejects empty email"

# Run specific test file
php artisan test tests/Feature/OrderTest.php

# Run tests in parallel
php artisan test --parallel

# Run with coverage
php artisan test --coverage

# Run and stop on first failure
php artisan test --stop-on-failure

# Run only dirty tests (changed files)
php artisan test --dirty

When Stuck

Debugging Integration

Bug found? Write failing test reproducing it. Follow TDD cycle. Test proves fix and prevents regression.

Never fix bugs without a test.

Final Rule

Production code → test exists and failed first
Otherwise → not TDD

No exceptions without your human partner's permission.