Can I use Laravel's Policy classes for mocking permissions in tests

Understanding Laravel Policies in Testing Context

Laravel Policies are designed to organize authorization logic around models or resources, defining methods that return boolean values indicating whether a user has permission to perform specific actions like viewing, updating, or deleting a resource. In testing, these policies represent the core of permission checks.

When testing authorization with policies, developers often want to verify that certain policy methods are called with the correct parameters and that the application reacts appropriately depending on the mock return values from these policy methods. However, because Laravel automatically registers policies and their methods are invoked within the framework's authorization layer, mocking them requires a specialized approach.

Mocking Laravel Policies

One approach to mocking policies in tests involves using Mockery or Laravel's built-in mocking helpers to create mocked instances of policy classes and binding them into the Laravel service container so that when the application calls for the policy, the mocked version is used instead of the actual policy implementation.

For example, Laravel's base test case class provides a `mock` method to create mocks conveniently and a `partialMock` method when only certain methods of the policy need to be mocked, allowing others to behave normally. This method is useful when wanting to override just a subset of policy behaviors while keeping the rest intact:

php
$policyMock = $this->partialMock(SomePolicy::class, function ($mock) {
    $mock->shouldReceive('viewAny')->andReturnFalse();
});

This mocked policy can now be tested to ensure that the authorization layer interacts with it as expected. This setup helps confirm that the system calls the correct policy methods under various scenarios.

Challenges in Mocking Policy Classes

A common challenge when trying to mock Laravel's policies is that policies are typically instantiated and registered early in the request lifecycle. As a result, simply mocking a policy class with Mockery or similar tools will not override the instance already registered with the Gate facade. This means Laravel might still use the actual policy class when resolving authorization during runtime in tests, ignoring the mocks.

To address this, tests can rebind the policy class into the Gate facade or the service container after mocking it to ensure that the framework uses the mock instead of the real class. Alternatively, some developers choose to mock the Gate facade methods themselves (e.g., `Gate::authorize` or `Gate::allows`). However, mocking the Gate facade directly can be more complex, especially when the user context is involved, such as in unit tests without logged-in users.

Testing Authorization with Policies: Unit vs Feature Tests

There is a distinction between unit and feature tests concerning policy testing:

- Unit Tests: These tests focus on the policy methods themselves. In this case, one typically instantiates the policy class directly and tests its methods with different user and model instances to assert correct authorization logic. This does not involve mocking because the actual policy logic is being tested.

- Feature Tests: These tests check how the policy integrates with the application flow, such as HTTP requests to controllers using `authorize` calls. Here, mocking policies can be valuable to test if the application routes or controllers call the expected policy methods and respond suitably to their outcomes (e.g., returning 403 Forbidden when authorization fails).

Recommended Approach for Mocking Policies in Tests

A practical and simpler approach involves creating a partial mock of the policy within a test and asserting expected behaviors without overly complex mocks or container rebindings. For example, one can partially mock a policy method to return `false` and then perform the HTTP request expecting a forbidden response, confirming that the controller is wired to the policy correctly:

php
$policyMock = $this->partialMock(SomePolicy::class);
$policyMock->expects('viewAny')->andReturnFalse();

$response = $this->get('/some-protected-route');
$response->assertForbidden();

This approach tests the connection between application layers while isolating authorization logic changes. The actual logic of the policy methods can be tested separately with more straightforward unit tests that operate directly on the policy instances.

Mocking Techniques Supported by Laravel

Laravel supports several mocking tools and techniques that aid in testing:

- Mocking Objects: Laravel provides the ability to mock objects injected via the service container by binding mocked instances to the container with `$this->instance()` or using the `$this->mock()` helper.

- Partial Mocking: This technique allows only some methods of a class to be mocked, while others operate normally, which is useful for policies where you want to control certain methods but keep the rest intact.

- Spying: Laravel also supports spies that record interactions and allow assertions afterward, useful to verify that the policy's methods were called with expected parameters.

- Mocking Facades: Since policies are used through Laravel's Gate facade, it is sometimes possible to mock calls on the Gate facade itself. This can be useful but might require more setup due to the nature of facades and user contexts.

Practical Examples and Considerations

To mock policy methods in tests, here is a sample workflow:

1. Partial Mock Policy Method: Use Laravel's `partialMock` helper to mock specific methods of the policy class during a test.

2. Bind the Mock: Bind this mock to the Laravel service container or ensure the Gate facade uses it.

3. Perform Authorization Check: Trigger an action in the application that invokes the authorization logic.

4. Assert Outcomes: Check if the policy method was called appropriately or that the application responded correctly (e.g., returned a 403 response).

When testing controller actions that use `$this->authorize()` internally, mocking policies this way confirms the integration without hitting actual database records or performing complex permission calculations.

Limitations and Best Practices

- Avoid mocking private or protected methods of policies unless absolutely necessary, as these are implementation details.

- Testing should balance between verifying the wiring of policies into the application versus validating the policy logic itself.

- In cases where policies are complex, consider writing dedicated unit tests for policy methods and minimal mocking for integration/feature tests.

- Keep tests maintainable by not tightly coupling them to internal policy method names unless it aligns with the test goal.

Summary

It is certainly feasible and sometimes beneficial to use Laravel's Policy classes for mocking permissions in tests. Using Laravel's built-in mocking helpers like `mock()` and `partialMock()`, policies can be mocked to simulate various authorization outcomes without invoking real authorization logic.

This allows tests to confirm that controllers or routes correctly enforce permissions based on policies and respond suitably to unauthorized access. However, because policies are registered early in the framework lifecycle, mocking requires binding mocked instances properly to override existing instances. Typically, a blend of policy unit tests (testing policy methods themselves) and feature tests with mocked policies provide a robust testing strategy for authorization.