Testing Helper

The Testing Helper provides functions to make testing of Hono applications easier.

Import

import { Hono } from 'hono'
import { testClient } from 'hono/testing'

testClient()

The testClient() function takes an instance of Hono as its first argument and returns an object typed according to your Hono application's routes, similar to the Hono Client. This allows you to call your defined routes in a type-safe manner with editor autocompletion within your tests.

Important Note on Type Inference:

For the testClient to correctly infer the types of your routes and provide autocompletion, you must define your routes using chained methods directly on the Hono instance.

The type inference relies on the type flowing through the chained .get(), .post(), etc., calls. If you define routes separately after creating the Hono instance (like the common pattern shown in the "Hello World" example: const app = new Hono(); app.get(...)), the testClient will not have the necessary type information for specific routes, and you won't get the type-safe client features.

Example:

This example works because the .get() method is chained directly onto the new Hono() call:

// index.ts
const app = new Hono().get('/search', (c) => {
  const query = c.req.query('q')
  return c.json({ query: query, results: ['result1', 'result2'] })
})

export default app

// index.test.ts
import { Hono } from 'hono'
import { testClient } from 'hono/testing'
import { describe, test, expect } from 'vitest' // Or your preferred test runner
import app from './app'

describe('Search Endpoint', () => {
  // Create the test client from the app instance
  const client = testClient(app)

  it('should return search results', async () => {
    // Call the endpoint using the typed client
    // Notice the type safety for query parameters (if defined in the route)
    // and the direct access via .$get()
    const res = await client.search.$get({
      query: { q: 'hono' },
    })

    // Assertions
    expect(res.status).toBe(200)
    expect(await res.json()).toEqual({
      query: 'hono',
      results: ['result1', 'result2'],
    })
  })
})