Does Keploy replace ExUnit + Phoenix.ConnTest?

No. Keep ExUnit + Phoenix.ConnTest 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 Phoenix 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 Phoenix 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 Phoenix testing framework

Keploy tests Phoenix 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 Phoenix tests free

keploy record -c "mix phx.server"

18.4K+

1.2M+300M+mocks createdSlack

What Keploy gives a Phoenix team

Any Phoenix service, unchanged

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

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

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The problem

Why Phoenix 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 Phoenix: by hand, with ExUnit + Phoenix.ConnTest, or with Keploy

ExUnit + Phoenix.ConnTest describes the exchange by hand and still needs the dependency supplied. Keploy records both halves once and replays them with nothing running.

By hand

ExUnit + Phoenix.ConnTest

With Keploy

Select any row for the full comparison, with code.

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Same coverage, three costs

What you write for Phoenix 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.exs

hand-written

defmodule AppWeb.OrderControllerTest do

use AppWeb.ConnCase, async: true

import Mox

setup :verify_on_exit!

test "confirms an order", %{conn: conn} do

# A behaviour-backed mock: no Postgrex, no rows.

expect(MockRepo, :find_order, fn "o-1" ->

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

end)

expect(MockPayments, :authorize, fn _ ->

{:ok, %{"status" => "AUTHORIZED"}}

end)

conn = post(conn, ~p"/orders/o-1/confirm")

assert json_response(conn, 200)["status"] == "CONFIRMED"

end

The Mox mock satisfies a behaviour, so Ecto never runs.

ExUnit + Phoenix.ConnTest1–2 hours

orders_bypass_test.exs

tool-assisted

defmodule AppWeb.OrderControllerBypassTest do

use AppWeb.ConnCase, async: false

setup do

bypass = Bypass.open()

# A real Cowboy endpoint, with a plug body you write.

Bypass.expect(bypass, "POST", "/v1/payment_intents/tok_123/confirm", fn conn ->

Plug.Conn.resp(conn, 200, ~s({"status":"AUTHORIZED"}))

end)

{:ok, bypass: bypass}

end

# Ecto's sandbox still needs a real database in the job.

test "confirms an order", %{conn: conn} do

conn = post(conn, ~p"/orders/o-1/confirm")

assert json_response(conn, 200)

end

ExUnit + Phoenix.ConnTest gives a real local endpoint. The database is still real too.

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

Phoenix testing tools, compared

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

Keploy

ExUnit + Mox

Bypass

Ecto SQL Sandbox

ExVCR

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 Phoenix app once, replay it forever

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

RecordingKeploy proxyeBPF · userspace

PostgreSQLPostgres protocol beneath the ORM

MySQLMySQL protocol beneath the driver

RedisRESP beneath the cache client

Outbound HTTPEvery outbound HTTP call

+2 more Phoenix 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 Phoenix, with zero config

5 of the 6 dependencies a typical Phoenix 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
RedisView page
RESP beneath the cache client
Outbound HTTP
Auto-mocked
Outbound HTTP
Every outbound HTTP call
Auto-mocked
Ecto
SQL beneath Ecto
Phoenix Channels
Partial
Phoenix Channels
WebSocket frames

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Quick start

Your first Phoenix test suite in under five minutes

Every command below runs against your existing Phoenix 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 "mix phx.server"
3
3Exercise the paths you care about
Use curl, your frontend, or an existing smoke script. Every request becomes a test case with its Phoenix calls captured alongside it.
curl -X POST localhost:4000/orders/o-1/confirm
curl localhost:4000/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 "mix phx.server" --delay 15