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Testing with createTestBus ​

Problem ​

Implement testing with createtestbus in a production-friendly way with @vielzeug/eventit while keeping setup and cleanup explicit.

Runnable Example ​

The snippet below is copy-paste runnable in a TypeScript project with @vielzeug/eventit installed.

ts
import { describe, it, expect } from 'vitest';
import { createTestBus } from '@vielzeug/eventit/test';

type CartEvents = {
  'item:added': { id: string; qty: number };
  'cart:cleared': void;
};

describe('cart module', () => {
  it('emits item:added when item is added', () => {
    using bus = createTestBus<CartEvents>();

    addItemToCart(bus, { id: 'sku-1', qty: 2 });

    expect(bus.emitted('item:added')).toEqual([{ id: 'sku-1', qty: 2 }]);
  });

  it('emits cart:cleared on reset', () => {
    using bus = createTestBus<CartEvents>();

    clearCart(bus);

    expect(bus.emitted('cart:cleared')).toHaveLength(1);
  });

  it('reset() clears emission records without removing listeners', () => {
    using bus = createTestBus<CartEvents>();

    addItemToCart(bus, { id: 'sku-1', qty: 1 });
    bus.reset();

    expect(bus.emitted('item:added')).toHaveLength(0);
  });
});

Expected Output ​

  • The example runs without type errors in a standard TypeScript setup.
  • The main flow produces the behavior described in the recipe title.

Common Pitfalls ​

  • Forgetting cleanup/dispose calls can leak listeners or stale state.
  • Skipping explicit typing can hide integration issues until runtime.
  • Not handling error branches makes examples harder to adapt safely.