Do I need Google Pub/Sub running to replay?

No. The recorded responses are served from the test set, so a replay run needs no Google Pub/Sub instance at all. You need it once, during the recording pass.

Is my Pub/Sub client still exercised?

Yes. Keploy replays at the protocol, so the client parses, converts and decodes exactly as it does in production. That is the difference from a stubbed client, which skips all of it.

How do I refresh the recordings?

Record again. One command re-captures every Google Pub/Sub interaction, so a schema or response change surfaces as a diff instead of a stale fixture that still passes.

Do I need GCP credentials to replay?

No. Replay serves recorded responses, so no credentials and no project are needed. You need them once, for the recording pass.

Does Keploy replace Testcontainers?

Not where you need the real engine, and that is worth being clear about. Use Testcontainers when a test genuinely has to exercise Google Pub/Sub itself. Keploy covers the much larger set of tests that only need the responses.

Keploy as a Google Pub/Sub testing framework

Keploy records the gRPC and HTTP API exchanges your service has with Google Pub/Sub, then replays them byte for byte in tests. Your Pub/Sub client runs unchanged and does its real work on every run, but CI needs no Google Pub/Sub instance, no schema and no seed data.

Generate Google Pub/Sub tests free

keploy record -c "<your app start command>"

18.5K+

1.2M+300M+mocks createdSlack

What Keploy gives a Google Pub/Sub team

Every Google Pub/Sub call your service makes

Keploy records the publish and pull exchanges your service has with Pub/Sub, so a message flow replays with no emulator and no GCP project.

gRPC and HTTP captured
Publish and pull kept
Ack and nack responses captured
No emulator in CI

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The problem

Why Google Pub/Sub 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 Google Pub/Sub: by hand, with Testcontainers, or with Keploy

Testcontainers gives a test a real Pub/Sub emulator at the cost of running one. A hand-written stub is cheap but never exercises the gRPC API. Keploy replays the recorded exchange with nothing running.

By hand

Testcontainers

With Keploy

Select any row for the full comparison, with code.

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Same coverage, three costs

What you write for Google Pub/Sub 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

order_repository_test.py

hand-written

from unittest.mock import MagicMock

# A stub Google Pub/Sub client: every reply is typed out here.

def test_reads_an_order():

client = MagicMock()

client.fetch.return_value = {

"id": "o-1",

"total": 4200,

"status": "NEW",

}

order = OrderRepository(client).find("o-1")

assert order.total == 4200

# Nothing here exercised the driver, so a type or encoding

# change in the real reply cannot fail this test.

A hand-written stub of the Google Pub/Sub client. The driver never runs.

Testcontainers1–2 hours

order_repository_container_test.py

tool-assisted

import pytest

from testcontainers.core.container import DockerContainer

@pytest.fixture(scope="session")

def client():

# Boots a real Google Pub/Sub per suite. Needs a Docker daemon

# available wherever the tests run, including CI.

with DockerContainer("gcr.io/google.com/cloudsdktool/google-cloud-cli:emulators") as c:

c.start()

yield connect(c.get_container_host_ip(), c.get_exposed_port(0))

def test_reads_an_order(client):

# Schema and seed data are still written by hand.

seed(client, id="o-1", total=4200, status="NEW")

order = OrderRepository(client).find("o-1")

assert order.total == 4200

Testcontainers runs the real Google Pub/Sub. Fidelity is genuine; the job pays for it.

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: gRPC

spec:

topic: orders.confirmed

records:

- { key: "o-1", value: '{"id":"o-1","status":"CONFIRMED"}' }

---

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

Google Pub/Sub testing tools, compared

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

Keploy

Testcontainers

Embedded Kafka

MockConsumer / MockProducer

LocalStack

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 Google Pub/Sub app once, replay it forever

Keploy sits below your Google Pub/Sub 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 Google Pub/Sub appGET/api/v1/orders/{id}200

RecordingKeploy proxyeBPF · userspace

JavaGoogle-cloud-pubsub

PythonGoogle-cloud-pubsub

Node.js@google-cloud/pubsub

GoCloud.google.com/go/pubsub

gRPCThe transport underneath

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 Google Pub/Sub, with zero config

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

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Quick start

Your first Google Pub/Sub test suite in under five minutes

Every command below runs against your existing Google Pub/Sub 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 "<your app start command>"
3
3Exercise the paths you care about
Use curl, your frontend, or an existing smoke script. Every request becomes a test case with its Google Pub/Sub 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 "<your app start command>" --delay 10