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WORKSHOP: API Integration testing
for Spring apps, with Testcontainers and WireMock
Oleg Nenashev, Gradle
Oleg Šelajev, Docker
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Async Q&A: Testcontainers and WireMock Slack
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Demo & Workshop repository
● github.com/oleg-nenashev/
spring_io_2025-Testcontainers-workshop
● Target app: Tracking the TODO list and
listing some news for your morning coffee!
NOTE: Trademarked names, project and company logos
belong to their respective owners
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We will use Gradle Build Tool
for the demo this time, Oleg
TL;DR: Two Olegs
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Oleg #1
Dr. Nenashev / Mr. Jenkins
Community Builder, Gradle
Developer Tools Hacker
@oleg_nenashev
oleg-nenashev
#RussiansAgainstPutin #StandWithUkraine
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Oleg #2
●
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Surprisingly, a Java Champion
18+ years software development experience
11 years Developer Advocate
Loves to stare at the code of Open Source projects
Quarkus
Spring Boot
LangChain4j
Microcks
Testcontainers (sometimes contributes bugs too!)
linkedin.com/in/shelajev/
youtube.com/user/shelajev/shorts
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What we talk about today?
1. Spring Dev Services
2. Testcontainers
3. WireMock
4. Everything together
5. Local models for modeling / testing AI
6. Integrations
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About You
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You Have a LOT to Integrate
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When IT Goes
wrong
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Do you `make it`?
IT - Integration Tests
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Today’s lab
The workshop!
On-demands:
● API Mocking 101
● Integration Testing 101
● Testcontainers 101
● WireMock 101
● Testing AI applications
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Before We Start
● Level of experience with tech we use
● Do you use Testcontainers?
● Do you use WireMock or Microcks?
● Do you already use Spring Boot Dev
Services?
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Want to follow along?
● A Laptop (?)
● Recommended: MacOS / Windows laptops
● Your Favorite IDE
● Docker Desktop
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Before we start
● docker model pull ai/gemma3-qat:1B-Q4_K_M
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101s
Integration & API Testing
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Spring Boot
and Dev Services
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See: Presentation by Moritz Halbritter
https://www.youtube.com/watch?v=Yqss7tYP890
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Options
● Manual Docker Compose & Co
● Dev Services with Docker Compose
● Dev Service with Testcontainers (!)
○ Test app with ./gradlew bootTestRun
https://docs.spring.io/spring-boot/reference/fe
atures/dev-services.html
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Integration Testing 101
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Integration Testing
● Multiple technology stacks
and toolchains
● Many teams involved
● Sacred knowledge
● [Almost] always too late
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APIs are the Key
for Developer Productivity
Client App
request
request
response
response
HTTP/2
API
API
Server
Storage
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API specs
API tech
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We will develop a custom framework
for integration tests
Just use xUnit
Just use xUnit
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Gaining confidence in you software
Build
Tests
“Shift Left”
with modern
tools
Integration tests
Build
Staging & QA
Tests
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https://martinfowler.com/articles/
mocksArentStubs.html
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Ways to do API integration testing
1. Testing against Production/Staging
servers
Accurate
Slow
Nope
Fast
2. Testing against a
simplified/containerized instance (e.g.
Testcontainers)
3. Modeling (aka Mocking) at the API
provider level (e.g. WireMock)
4. Mocking at the code level
* For Testcontainers, see the slides
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Ways to do API integration testing
1. Testing against Production/Staging servers
Accurate
Slow
Nope
Fast
2. Testing against a simplified/containerized
instance (e.g. Testcontainers)
3. Modeling (aka Mocking) at the API provider
level (e.g. WireMock or Microcks)
4. Mocking at the code level
* For Testcontainers, see the slides
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Testcontainers 101
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Example
- Java
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https://testcontainers.com/modules/
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LOCAL STACK
https://testcontainers.com/modules/
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SDKs
testcontainers.org
… and
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github.com/testcontainers/
testcontainers-go
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WireMock 101
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No Implementation?
Fake it until you “$ make it”
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Ways to do API integration testing
1. Testing against Production/Staging servers
Accurate
Slow
Nope
Fast
2. Testing against a simplified/containerized
instance (e.g. Testcontainers)
3. Modeling (aka Mocking) at the API
provider level (e.g. WireMock or Microcks)
4. Mocking at the code level
* For Testcontainers, see the slides
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API Mocking for Java. Examples
Open Source
Proprietary
`
en.wikipedia.org/wiki/Comparison_of_API_simulation_tools
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API Mocking Tools
Main implementation in Java
Sandbox CNCF Project
Native lib, Docker images and
Testcontainers modules
Golang / Microservice arch
Support for GraalVM
Docker image, Testcontainers
module, All-in K8s Charts
Rich Ecosystem
Less Rich Ecosystem
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API Mocking 101
WireMock Config JSON:
IF (request_url)
THEN (response) *
Client
library
request
response
HTTP/2
Client App
Mock API Server
* it gets MUCH more complex
wiremock.org/docs/stubbing
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WireMock Ecosystem & Features
wiremock.org/docs
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WireMock Ecosystem
Gradle
Build Tool
wiremock.org/docs
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WireMock in Java
wiremock.org/docs/stubbing
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WireMock Ecosystem / Java
● Java
● Kotlin
● Scala
● Groovy
● Clojure
● (?)Android
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JUnit 4/5
Testcontainers
Sprint Boot
Spring Cloud Contract
Quarkus
Maven / Gradle Build Tool
Spock
Pact
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Example
- JUnit 5
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WireMock Plugin for Gradle Build Tool
William-Hill-Online/wiremock-gradle-plugin
Gradle
Build Tool
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WireMock for Spring Boot
● There is a library for it!
● https://wiremock.org/docs/solutions/
spring-boot-integration/
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WireMock has an official Testcontainers module!
testcontainers.com/modules/wiremock
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Demos
● https://github.com/wiremock/wiremock-docker
● https://github.com/oleg-nenashev/mocks-as-code-demo
● https://github.com/wiremock/wiremock-grpc-demos
● https://github.com/wiremock/wiremock-spring-boot-oauth2-demo
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WireMock or
Testcontainers?
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Choosing a right tool *
● Need database or complex dynamic environment?
○
YES => Testcontainers
● Do you have a ready implementation?
○
NO => WireMock/Microcks
● Is it containerized and lightweight?
○
NO => WireMock/Microcks
● Can you easily trigger the desired scenarios?
○
NO => WireMock/Microcks
● Else: => Testcontainers
* Likely, you
want to use both
* Your mileage may vary
** More later
*** I just like footnotes
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WireMock has an official Testcontainers module!
testcontainers.com/modules/wiremock
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Proxy can be made transparent in your test!
Tests
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WireMock Proxy? Why?
● Record & Playback for Request sequences
● Reverse engineering of legacy undocumented APIs
● NEW: OpenAPI Standard Compliance Verification (in 3.0 Beta)
● Emulating complex cases
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Overriding particular responses
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Emulating response sequences / Stateful behavior
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Failure Injection
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More Demos
● Simple WireMock and Testcontainers demo:
github.com/testcontainers-community/testcontainers-wiremock-demo
● WireMock and Docker integration tests:
https://github.com/wiremock/wiremock-docker
● Quarkus Dev Service for WireMock and Testcontainers:
https://github.com/oleg-nenashev/gradle-quarkus-plugin-demo
● Spring Boot + Testcontainers and WireMock + LocalStack:
https://github.com/oleg-nenashev/mocks-as-code-demo
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Docker Model Runner
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Docker Model Runner
➔
Run models locally with full GPU support
➔
Distribute models through container registries
➔
Easily integrate using any OpenAI-compatible SDKs and libraries
compose.yaml
services:
llm:
provider:
type: model
options:
model: ai/gemma3:4B-F16
app:
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Resources
● Docker Model Runner docs:
https://docs.docker.com/model-runner/
● Using Docker Model in Docker Compose
https://docs.docker.com/compose/how-tos/model-runner/#provider-services
● Using Docker Model Runner for AI assistant setup:
https://dev.to/olegshelajev/easy-private-ai-assistant-with-goose-and-docker-model-runner-4b41
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Lessons Learned
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Takeaways
● Shift left the integration testing
● API Mocking / abstraction are great…
when used right
● There is no silver bullet
● WireMock and Testcontainers address
their own use-cases
● They work well together!
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Choosing a right tool *
● Need database or complex dynamic environment?
○
YES => Testcontainers
● Do you have a ready implementation?
○
NO => WireMock/Microcks
● Is it containerized and lightweight?
○
NO => WireMock/Microcks
● Can you easily trigger the desired scenarios?
○
NO => WireMock/Microcks
● Else: => Testcontainers
* Likely, you
want to use both
* Your mileage may vary
** More later
*** I just like footnotes
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Keep Learning Tools
* AKA: Burning Out 101
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It’s [always] a great time to contribute!
testcontainers.org/contributing
wiremock.org/participate
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Questions?
Testcontainers Slack
WireMock Slack
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