msw-trpc

---

tPRC support for MSW

• Create MSW handlers from your tRPC router.
• Get your tRPC typing into your MSW handlers.
• Augments MSW with utils for tRPC.

Motivation

As someone who loves MSW and was already using it I wanted to keep using it instead of mocking tRPC. While it is possible to simply write the Rest handlers it felt like it would be great not to lose the full power of tRPC types in the tests.

Usage

1. Install msw-trpc.

npm i msw-trpc --save-dev

2. build your trpcMsw with createTRPCMsw.

import { createTRPCMsw } from 'msw-trpc'
import type { AppRouter } from 'path/to/your/router'

export const trpcMsw = createTRPCMsw<AppRouter>() /* 👈 */

3. Start using it.

const server = setupServer(
  trpcMsw.userById.query((req, res, ctx) => {
    return res(ctx.status(200), ctx.data({ id: '1', name: 'Uncle bob' }))
  }),
  trpcMsw.createUser.mutation(async (req, res, ctx) => {
    return res(ctx.status(200), ctx.data({ id: '2', name: await req.json() }))
  })
)

How it works

createTRPCMsw returns a Proxy that infers types from your AppRouter

// all queries will expose a query function that accepts a MSW handler
trpcMsw.myQuery.query((req, res, ctx) => {})

// all mutations will expose a mutation function that accepts a MSW handler
trpcMsw.myMutation.mutation((req, res, ctx) => {})

supports merged routers

// @filename: routers/_app.ts
// taken from https://trpc.io/docs/merging-routers
import { userRouter } from './user'
import { postRouter } from './post'

const appRouter = router({
  user: userRouter, // put procedures under "user" namespace
  post: postRouter, // put procedures under "post" namespace
})

// @filename: frontend/test/PostList.tsx

// all nested routers will be infered properly
trpcMsw.user.list.query((req, res, ctx) => {})

MSW Augments

ctx.data

Inspired by MSW GraphQL the context of your handlers now exposes a data function that will transform your data to the tRPC structure

mswTrpc.userById.query((req, res, ctx) => {
  console.log(ctx.data({ my: 'data' })) /* 👈 */
})

// return ctx.json with
{
  result: {
    data: {
      my: 'data'
    }
  }
}

req.getInput

Returns the parsed input from the request

//router.ts
const appRouter = t.router({
  userById: t.procedure.input(z.object({ name: z.string() })).query(req => {
    const { input } = req
    const user = userList.find(u => u.name === input.name)
    return user
  }),
})

//test-file.ts
mswTrpc.userById.query((req, res, ctx) => {
  console.log(req.getInput()) /* 👈 */
})

mswTrpc.createUser.mutation(async (req, res, ctx) => {
  console.log(await req.getInput()) /* 👈 in mutation handle getInput returns a promise because it uses req.json() */
})

// outputs
{
  name: 'Pedro'
}

test('should do something', () => {
  trpc.userById.query({ name: 'Pedro' })
})

Please note:

• calling req.getInput and req.json in the same mutation handler will fail

Config

createTRPCMsw accepts a 2nd argument:

type config = {
  basePath?: string
  baseUrl?: string
  transformer?: {
    input: {
      serialize(object: any): any
      deserialize(object: any): any
    }
    output: {
      serialize(object: any): any
      deserialize(object: any): any
    }
  }
}

property	default	details
basePath	'trpc'	Will match all requests to basePath regardless of host
baseUrl	undefined	Setting this overrides basePath and will only match requests to this specific baseUrl
transformer	defaultTransformer	Will transform your output data with transformer.output.serialize when calling ctx.data

Requirements

Peer dependencies:

• tRPC server v10 (@trpc/server) must be installed.
• msw (msw) must be installed.

Please note:

• Batch is not yet supported
• Merged routers will match in MSW against . or / (I'm open to PRs on how to only match against . 😊 )

mswTrpc.user.list.query() // this will match /trpc/user/list and /trpc/user.list