MockComponent API

Asena's built-in testing utilities provide automated dependency mocking for components using dependency injection. The mockComponent and mockComponentAsync functions automatically discover and mock all injected dependencies.

Quick Start

import { mockComponent } from '@asenajs/asena/test';
import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';
import { mock } from 'bun:test';

@Service()
class UserService {
  async createUser(name: string, email: string): Promise<{ id: string; name: string; email: string }> {
    // implementation
  }
}

@Service()
class AuthService {
  @Inject(UserService)
  private userService!: UserService;

  async register(name: string, email: string, password: string) {
    const user = await this.userService.createUser(name, email);
    return { user, token: 'jwt-token' };
  }
}

// Test
describe('AuthService', () => {
  test('should register user', async () => {
    const { instance, mocks } = mockComponent(AuthService);

    // Configure mock behavior
    mocks.userService.createUser.mockResolvedValue({
      id: 'user-123',
      name: 'John Doe',
      email: 'john@example.com'
    });

    // Test
    const result = await instance.register('John', 'john@example.com', 'pass');

    expect(result.user.id).toBe('user-123');
    expect(mocks.userService.createUser).toHaveBeenCalledWith('John', 'john@example.com');
  });
});

API Reference

mockComponent

Creates a component instance with all dependencies automatically mocked.

function mockComponent<T extends object>(
  ComponentClass: new (...args: any[]) => T,
  options?: MockComponentOptions
): MockedComponent<T>

Parameters:

• ComponentClass - The component class to instantiate
• options - Optional configuration (see MockComponentOptions)

Returns: MockedComponent<T>

Example:

const { instance, mocks } = mockComponent(PaymentService);

mockComponentAsync

Asynchronous version of mockComponent for components with async postConstruct hooks.

async function mockComponentAsync<T extends object>(
  ComponentClass: new (...args: any[]) => T,
  options?: MockComponentOptions
): Promise<MockedComponent<T>>

Parameters: Same as mockComponent

Returns: Promise<MockedComponent<T>>

Example:

import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';

@Service()
class ConnectionPool {
  async connect() {
    // implementation
  }
}

@Service()
class DatabaseService {
  @Inject(ConnectionPool)
  private pool!: ConnectionPool;

  async initialize() {
    await this.pool.connect();
  }
}

const { instance, mocks } = await mockComponentAsync(DatabaseService, {
  postConstruct: async (inst) => {
    await inst.initialize();
  }
});

MockComponentOptions

Configuration options for component mocking.

interface MockComponentOptions {
  // Only mock specific fields (optional)
  injections?: string[];

  // Provide custom mocks instead of auto-generated ones (optional)
  overrides?: Record<string, any>;

  // Your own callback, run after injection (optional, can be async).
  // NOT the component's @OnStart - see below
  postConstruct?: (instance: any) => void | Promise<void>;
}

Properties:

injections

Array of field names to mock. Other fields will not be mocked.

const { instance, mocks } = mockComponent(PaymentService, {
  injections: ['stripe'] // Only mock stripe
});

expect(mocks.stripe).toBeDefined();
expect(mocks.logger).toBeUndefined();

overrides

Custom mock objects to use instead of auto-generated mocks.

import { mock } from 'bun:test';

const customMock = {
  createUser: mock(async () => ({ id: 'custom-id' }))
};

const { instance, mocks } = mockComponent(AuthService, {
  overrides: { userService: customMock }
});

// mocks.userService is now your custom mock
expect(mocks.userService).toBe(customMock);

An override is the final value injected into the field:

• For expression-based injections (e.g. @Inject(ulak('/chat')) or @Inject(UserService, (s) => s.createUser)), the expression is skipped entirely — your override is used as-is.
• Presence is checked with Object.hasOwn, so falsy values (0, '', null, undefined) are injected as-is rather than ignored.

postConstruct

A callback of yours, run after the dependencies are injected.

const { instance, mocks } = mockComponent(AuthService, {
  postConstruct: (instance) => {
    console.log('Component ready for testing');
  }
});

It is not the component's @OnStart

mockComponent builds the instance directly — it never goes through the container or the server, so the component's own @OnStart / @OnStop hooks are not invoked. This option is the hook you would otherwise write inline; if you want the real start hook, call it yourself:

const { instance } = await mockComponentAsync(DatabaseService, {
  postConstruct: async (inst) => inst.onStart(),   // the @OnStart method, called explicitly
});

For hooks running in their real order against a real container, use createTestApp.

Async Support

The postConstruct hook can be async. Use mockComponentAsync when you need to await the hook.

MockedComponent<T>

Return type of mockComponent and mockComponentAsync.

interface MockedComponent<T> {
  instance: T;                // Component instance with injected mocks
  mocks: Record<string, any>; // Object containing all mock dependencies
}

Properties:

• instance - The component instance with all dependencies injected
• mocks - Object where keys are field names and values are mock objects

Advanced Usage Patterns

Selective Mocking

Mock only specific dependencies while leaving others undefined.

import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';

@Service()
class StripeClient {
  async charge(amount: number) {
    // implementation
  }
}

@Service()
class LoggerService {
  log(message: string) {
    // implementation
  }
}

@Service()
class PaymentService {
  @Inject(StripeClient)
  private stripe!: StripeClient;

  @Inject(LoggerService)
  private logger!: LoggerService;
}

const { instance, mocks } = mockComponent(PaymentService, {
  injections: ['stripe'] // Only mock stripe, logger remains undefined
});

expect(mocks.stripe).toBeDefined();
expect(mocks.logger).toBeUndefined();

Custom Overrides

Provide your own mock implementations for specific dependencies.

import { mock } from 'bun:test';

const customUserService = {
  createUser: mock(async (name: string, email: string) => ({
    id: 'custom-id',
    name,
    email
  })),
  deleteUser: mock(async (id: string) => true)
};

const { instance, mocks } = mockComponent(AuthService, {
  overrides: {
    userService: customUserService
  }
});

// mocks.userService is now your custom mock
expect(mocks.userService).toBe(customUserService);

Combining Options

You can combine injections, overrides, and postConstruct together.

const { instance, mocks } = mockComponent(AuthService, {
  injections: ['userService', 'emailService'],
  overrides: {
    userService: customUserService
  },
  postConstruct: (inst) => {
    inst.setTestMode(true);
  }
});

Expression Transformations

mockComponent supports @Inject expression transformations automatically. When an expression field is not overridden, the expression is evaluated against a deep mock: every property access yields a Bun mock function and every call returns another chainable deep mock, so any expression works without a running application.

import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';

@Service()
class UserService {
  async createUser(name: string, email: string): Promise<{ id: string; name: string; email: string }> {
    // implementation
  }
}

@Service()
class AuthService {
  @Inject(UserService, (service) => service.createUser)
  private createUserFn!: (name: string, email: string) => Promise<User>;
}

const { instance, mocks } = mockComponent(AuthService);

// The expression is applied automatically - createUserFn is a real Bun mock
mocks.createUserFn.mockResolvedValue({ id: 'user-123' });

expect(mocks.createUserFn).toHaveBeenCalledWith('John', 'john@example.com');

If the field is provided via overrides, the expression is skipped and your override is injected as-is.

Testing Services with Ulak Injections

Services that inject scoped namespaces with the ulak() helper are testable without a running WebSocket broker.

import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';
import { ulak, type Ulak } from '@asenajs/asena/messaging';

@Service('UserService')
export class UserService {
  @Inject(ulak('/ws/public/stats'))
  private statsChannel: Ulak.NameSpace<'/ws/public/stats'>;

  async createAnonUser(name: string) {
    // ...create the user...
    await this.statsChannel.broadcast({ action: 'update', data: { newUser: 1 } });
  }
}

Variant A — automatic deep mock. No configuration needed; the namespace methods are assertable Bun mocks:

import { describe, expect, test } from 'bun:test';
import { mockComponent } from '@asenajs/asena/test';

test('broadcasts stats on user creation', async () => {
  const { instance, mocks } = mockComponent(UserService);

  await instance.createAnonUser('John');

  expect(mocks.statsChannel.broadcast).toHaveBeenCalledWith({
    action: 'update',
    data: { newUser: 1 }
  });
});

Variant B — typed stub via createTestUlakStub. Use an explicit override when you want a fully typed Ulak.NameSpace mock:

import { createTestUlakStub, mockComponent } from '@asenajs/asena/test';

test('broadcasts stats on user creation', async () => {
  const statsChannel = createTestUlakStub('/ws/public/stats');

  const { instance } = mockComponent(UserService, {
    overrides: { statsChannel }
  });

  await instance.createAnonUser('John');

  expect(statsChannel.broadcast).toHaveBeenCalledWith({
    action: 'update',
    data: { newUser: 1 }
  });
});

TIP

createTestUlakStub implements the full Ulak.NameSpace interface (broadcast, to, toSocket, toMany, getSocketCount) with Bun mocks, so it stays in sync with the framework at compile time.

Testing Components with Inheritance

mockComponent properly handles prototype chains.

import { Service } from '@asenajs/asena/decorators';
import { Inject } from '@asenajs/asena/decorators/ioc';

@Service()
class LoggerService {
  log(message: string) {
    // implementation
  }
}

@Service()
class DatabaseService {
  query(sql: string) {
    // implementation
  }
}

@Service()
class BaseService {
  @Inject(LoggerService)
  protected logger!: LoggerService;
}

@Service()
class UserService extends BaseService {
  @Inject(DatabaseService)
  private database!: DatabaseService;
}

const { instance, mocks } = mockComponent(UserService);

// Both inherited and own dependencies are mocked
expect(mocks.logger).toBeDefined();
expect(mocks.database).toBeDefined();

Technical Details

How It Works

1. Metadata Discovery - Reads the same metadata that Asena's IoC Container uses (ComponentConstants.DependencyKey, ComponentConstants.DependencyClassKey and ComponentConstants.ExpressionKey)
2. Mock Generation - Uses Bun's native mock() function to create mocks
   • Automatically detects async methods and creates mock(async () => null)
   • Sync methods get mock(() => undefined)
3. Injection - Injects mocks into the component instance
4. Expression Support - Evaluates expression transformations against a deep mock (unless the field is overridden, in which case the override is injected as-is)

What each field receives

The mock a field gets depends on how it was injected:

Injection	Mock
@Inject(UserService)	An object shaped like the class — every method is a bun:test mock
@Inject(ulak('/chat')) and other expression injections	The expression evaluated against a deep mock, so any call chain works and stays assertable
@Inject('UserService')	A plain {} — a string carries no class reference, so no method shape can be derived

String injections need overrides

Only class-based injections can be auto-shaped. For @Inject('UserService') pass the double yourself:

mockComponent(LegacyService, {
  overrides: { userService: { findById: mock(async () => ({ id: '1' })) } },
});

Zero Dependencies

This feature follows Asena's zero-dependency philosophy:

• Uses only Bun's native mock() function from bun:test
• No external testing libraries required
• Fully compatible with Bun's test runner

Import Path

import {
  mockComponent,
  mockComponentAsync,
  createMockFromClass,
  createDeepMock,
  createTestUlakStub
} from '@asenajs/asena/test';

Package export configuration:

{
  "exports": {
    "./test": {
      "import": "./dist/lib/test/index.js",
      "types": "./dist/lib/test/index.d.ts"
    }
  }
}

Related

• Testing Overview - Introduction to testing in Asena
• createTestApp - Full-application testing with real HTTP
• createWebTest - Controller-slice testing (note: mocks there is keyed by service name, not field name)
• Examples - Real-world testing patterns
• Dependency Injection - Understanding DI in Asena
• Bun Test Documentation - Learn more about Bun's test runner