Does Keploy replace bun test?

No. Keep bun test for unit tests, where it is the right tool. Keploy covers the integration layer, where the cost is the dependencies rather than the assertions.

Do I have to change my Bun code?

No. Keploy runs the process you already run and captures at the socket, so no annotation, no wrapper and no dependency injection change is needed.

What happens when a dependency changes?

Re-record. One command refreshes every captured interaction in the suite, so a changed contract shows up as a diff rather than as a silently passing stale mock.

Is Bun's speed advantage lost?

No. Replay adds no dependency boot at all, so a Keploy run is usually faster than the same suite against a container, and it keeps Bun's own start time.

Can I run this in CI?

Yes, and that is the point: replay needs nothing running. No database service, no broker, no network access to upstreams, so the job is the same on every runner.

Keploy as a Bun testing framework

Keploy tests Bun services by recording real HTTP and database traffic from a running process, then replaying it as assertions. There is no module mock to register and nothing to mock by hand, because capture happens below the runtime at the socket.

Generate Bun tests free

keploy record -c "bun run index.ts"

18.4K+

1.2M+300M+mocks createdSlack

What Keploy gives a Bun team

Any Bun service, unchanged

Keploy runs the process you already run with bun. Elysia, Hono and a bare Bun.serve handler all record identically.

Bun 1.x
Elysia, Hono, Bun.serve
Node-compatible packages
No bunfig changes

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The problem

Why Bun integration tests slow teams down

The friction is rarely the assertions. It is everything around them — spinning up dependencies, keeping mocks honest, and repairing tests after every refactor.

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Three ways to do it

Testing Bun: by hand, with bun test, or with Keploy

bun test describes the exchange by hand and still needs the dependency supplied. Keploy records both halves once and replays them with nothing running.

By hand

bun test

With Keploy

Select any row for the full comparison, with code.

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Same coverage, three costs

What you write for Bun vs what Keploy records

All three produce the same assertion. Only the third still passes after the next refactor without anyone editing it.

By hand2–4 hours

orders.test.ts

hand-written

import { test, expect, mock } from "bun:test";

import { handler } from "./orders";

// Swapped in the module registry for the whole file.

mock.module("./db", () => ({

findOrder: async () => ({ id: "o-1", total: 4200, status: "NEW" }),

}));

mock.module("./payments", () => ({

authorize: async () => ({ status: "AUTHORIZED" }),

}));

test("confirms an order", async () => {

const res = await handler(new Request("http://localhost/orders/o-1/confirm", {

method: "POST",

}));

expect(res.status).toBe(200);

});

bun:test mocks the module, so the Postgres driver never runs.

bun test1–2 hours

orders.integration.test.ts

tool-assisted

import { test, expect } from "bun:test";

import { SQL } from "bun";

import { handler } from "./orders";

// A real Postgres, so the job needs one running.

const db = new SQL(process.env.DATABASE_URL!);

await db`insert into orders values ('o-1', 4200, 'NEW')`;

// A stub upstream, which the handler must be pointed at.

const stub = Bun.serve({

port: 8787,

fetch: () => new Response(JSON.stringify({ status: "AUTHORIZED" })),

});

test("confirms an order", async () => {

process.env.PAYMENTS_URL = "http://localhost:8787";

const res = await handler(new Request("http://localhost/orders/o-1/confirm", {

method: "POST",

}));

expect(res.status).toBe(200);

});

A stub upstream on a real port, and a real database to seed.

With Keploy~5 minutes

keploy/test-set-0/test-1.yaml

auto-generated

version: api.keploy.io/v1beta1

kind: Http

name: test-1

spec:

req:

method: POST

url: /orders/o-1/confirm

resp:

status_code: 200

body: '{"id":"o-1","status":"CONFIRMED","total":4200}'

assertions:

noise:

- body.confirmedAt

---

kind: Postgres

spec:

query: select id, total, status from orders where id = $1

rows:

- { id: "o-1", total: 4200, status: "NEW" }

---

kind: Http

spec:

request:

url: https://api.payments.example.com/v1/payment_intents/tok_123/confirm

response:

body: '{"status":"AUTHORIZED"}'

Recorded from one real request. Nothing here was typed by hand.

Times are estimates for authoring one endpoint’s coverage from scratch, not measurements.

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Keploy vs the alternatives

Bun testing tools, compared

The options a team on Node.js actually reaches for, and where each one genuinely wins. Select a row for the full comparison.

Keploy

Jest + supertest

nock

Mocha + Sinon

Mock Service Worker

Postman

SmartBear ReadyAPI

Best in classStrongPartialNot covered

Assessments reflect each tool’s documented behaviour, not benchmark measurements.

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How it works

Record your Bun app once, replay it forever

Keploy sits below your Bun process at the network layer. It watches the calls your app already makes, then serves them back on replay so tests run with no dependencies attached.

Your Bun appGET/api/v1/orders/{id}200

RecordingKeploy proxyeBPF · userspace

PostgreSQLPostgres protocol beneath Bun.sql and pg

MySQLMySQL protocol beneath mysql2

SQLiteQueries through bun:sqlitePartial

RedisRESP beneath ioredis

+2 more Bun dependencies

An example shape of a captured call. Your own endpoints and dependencies come from your real traffic, so nothing here has to be written by hand.

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Mock coverage

What Keploy mocks for Bun, with zero config

5 of the 6 dependencies a typical Bun service talks to are stubbed from the recording itself — no mock classes, no fixture files, no containers in CI.

Auto-mocked
PostgreSQLView page
Postgres protocol beneath Bun.sql and pg
Auto-mocked
MySQLView page
MySQL protocol beneath mysql2
Partial
SQLiteView page
Queries through bun:sqlite
Auto-mocked
RedisView page
RESP beneath ioredis
Auto-mocked
MongoDBView page
Wire protocol beneath the Mongo driver
Outbound HTTP
Auto-mocked
Outbound HTTP
Every fetch call

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Quick start

Your first Bun test suite in under five minutes

Every command below runs against your existing Bun service. Nothing in your source tree changes.

1
1Install the Keploy CLI
A single binary. It needs a Linux kernel with eBPF support, or Docker on macOS and Windows — and it adds nothing to your project's dependencies.
curl -sSL https://keploy.io/install.sh | bash
2
2Record your service
Pass the command you already use to start the app. Keploy runs it and watches every socket it opens.
keploy record -c "bun run index.ts"
3
3Exercise the paths you care about
Use curl, your frontend, or an existing smoke script. Every request becomes a test case with its Bun calls captured alongside it.
curl -X POST localhost:3000/orders/o-1/confirm
curl localhost:3000/orders/o-1
4
4Replay in CI
Replay serves the recorded dependency responses, so the job needs no service containers and no Docker daemon.
keploy test -c "bun run index.ts" --delay 10