tRPC•5mo ago

how to best test trpc?

does programs like postman not work well with trpc? if i wanted to test my trpc server by making requests, what the best way to do that?

y_nk•8/8/25, 2:59 PM

i've found that best is to use the trpc client in your test runner (vitest/jest) by setting up the trpc client to use a custom http link which uses supertestsupertest with your app passed as param.

with fastify (but it works with express too):

export function createTestClient(app: FastifyInstance) {
  const agent = supertest.agent(app.server)

  return createTRPCClient<AppRouter>({
    links: [
      httpLink({
        transformer: superjson,
        url: 'http://localhost/api',
        async fetch(input, options) {
          const method = options?.method?.toLowerCase() ?? 'get'
          const url = new URL(input)

          let call = agent[method](`${url.pathname}${url.search}`)

          // Add headers
          if (options?.headers) {
            for (const [key, val] of Object.entries(options.headers)) {
              call = call.set(key, val)
            }
          }

          if (options?.body) {
            call = call.send(options.body)
          }

          const res = await call

          return new Response(JSON.stringify(res.body), {
            status: res.status,
            headers: res.headers,
          })
        },
      }),
    ],
  })
}

export function createTestClient(app: FastifyInstance) {
  const agent = supertest.agent(app.server)

  return createTRPCClient<AppRouter>({
    links: [
      httpLink({
        transformer: superjson,
        url: 'http://localhost/api',
        async fetch(input, options) {
          const method = options?.method?.toLowerCase() ?? 'get'
          const url = new URL(input)

          let call = agent[method](`${url.pathname}${url.search}`)

          // Add headers
          if (options?.headers) {
            for (const [key, val] of Object.entries(options.headers)) {
              call = call.set(key, val)
            }
          }

          if (options?.body) {
            call = call.send(options.body)
          }

          const res = await call

          return new Response(JSON.stringify(res.body), {
            status: res.status,
            headers: res.headers,
          })
        },
      }),
    ],
  })
}

export function createTestClient(app: FastifyInstance) { const agent = supertest.agent(app.server) return createTRPCClient<AppRouter>({ links: [ httpLink({ transformer: superjson, url: 'http://localhost/api', async fetch(input, options) { const method = options?.method?.toLowerCase() ?? 'get' const url = new URL(input) let call = agent[method](`${url.pathname}${url.search}`) // Add headers if (options?.headers) { for (const [key, val] of Object.entries(options.headers)) { call = call.set(key, val) } } if (options?.body) { call = call.send(options.body) } const res = await call return new Response(JSON.stringify(res.body), { status: res.status, headers: res.headers, }) }, }), ], }) }