Does Keploy replace kotlin.test + testApplication?

No. Keep kotlin.test + testApplication 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 Ktor 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.

Does it work with Ktor middleware?

Yes, and that is a reason to prefer recording here: middleware, authentication and serialisation all run on every recorded request, so the test covers the real request path rather than a handler called directly.

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 Ktor testing framework

Keploy tests Ktor services by recording real HTTP and database traffic from a running process, then replaying it as assertions. There is no test context to assemble and no framework wiring to change, because capture happens below the framework at the socket.

Generate Ktor tests free

keploy record -c "java -jar build/libs/app.jar"

18.4K+

1.2M+300M+mocks createdSlack

What Keploy gives a Ktor team

Any Ktor service, unchanged

Keploy runs the Ktor process unchanged. Routing, middleware and serialisation all execute on every recorded request, because capture is at the socket rather than inside the framework.

Any Ktor version
Middleware runs unchanged
Routing and serialisation real
No plugin or adapter

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The problem

Why Ktor 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 Ktor: by hand, with kotlin.test + testApplication, or with Keploy

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

By hand

kotlin.test + testApplication

With Keploy

Select any row for the full comparison, with code.

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Same coverage, three costs

What you write for Ktor 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

OrderRoutesTest.kt

hand-written

import io.ktor.server.testing.*

import kotlin.test.Test

import kotlin.test.assertEquals

// Hand-written fakes: no Exposed, no rows, no type conversion.

class FakeOrderRepository : OrderRepository {

override suspend fun find(id: String) = Order(id, 4200, "NEW")

}

class FakePayments : PaymentClient {

override suspend fun authorize(token: String) = Auth("AUTHORIZED")

}

class OrderRoutesTest {

@Test

fun `confirms an order`() = testApplication {

application { module(FakeOrderRepository(), FakePayments()) }

val res = client.post("/orders/o-1/confirm")

assertEquals(200, res.status.value)

}

The fakes return Kotlin objects, so Exposed never issues a statement.

kotlin.test + testApplication1–2 hours

OrderRoutesMockEngineTest.kt

tool-assisted

import io.ktor.client.engine.mock.*

import io.ktor.server.testing.*

import kotlin.test.Test

class OrderRoutesMockEngineTest {

@Test

fun `confirms an order`() = testApplication {

// One handler per outbound URL, written by hand.

val engine = MockEngine { request ->

respond(

content = """{"status":"AUTHORIZED"}""",

headers = headersOf(HttpHeaders.ContentType, "application/json"),

)

}

// A real Postgres is still needed for the Exposed half.

application { module(exposedRepository(), HttpClient(engine)) }

val res = client.post("/orders/o-1/confirm")

assertEquals(200, res.status.value)

}

Ktor's MockEngine covers the client half. The database is still real.

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

Ktor testing tools, compared

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

Keploy

JUnit + Mockito

WireMock

REST Assured

Testcontainers

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 Ktor app once, replay it forever

Keploy sits below your Ktor 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 Ktor appGET/api/v1/orders/{id}200

RecordingKeploy proxyeBPF · userspace

PostgreSQLPostgres protocol beneath the ORM

MySQLMySQL protocol beneath the driver

MongoDBWire protocol beneath the Mongo driver

RedisRESP beneath the cache client

+2 more Ktor 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 Ktor, with zero config

6 of the 6 dependencies a typical Ktor 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 the ORM
Auto-mocked
MySQLView page
MySQL protocol beneath the driver
Auto-mocked
MongoDBView page
Wire protocol beneath the Mongo driver
Auto-mocked
RedisView page
RESP beneath the cache client
Outbound HTTP
Auto-mocked
Outbound HTTP
Every outbound HTTP call
Auto-mocked
Exposed
SQL beneath Exposed

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Quick start

Your first Ktor test suite in under five minutes

Every command below runs against your existing Ktor 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 "java -jar build/libs/app.jar"
3
3Exercise the paths you care about
Use curl, your frontend, or an existing smoke script. Every request becomes a test case with its Ktor calls captured alongside it.
curl -X POST localhost:8080/orders/o-1/confirm
curl localhost:8080/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 "java -jar build/libs/app.jar" --delay 15