Mocks as code: Modeling AWS service providers with Testcontainers, WireMock and Localstack

When managing services at scale, you need automated testing while mocking (or modeling) the parts provided by public clouds, as well as testing entire deployment processes. This session demonstrates how to combine Localstack (for AWS integration testing), WireMock (for service mocking), and Testcontainers, a popular framework for Docker and other container engines, for comprehensive integration testing - all running in a Dev Container on your local machine.

Using Pulumi and Java as examples, you'll see live coding that demonstrates how these tools work together, with the approach applicable to any tech stack. Expect a hands-on workshop format with minimal tool requirements, showcasing developer experience for modern, containerized developer environments and practical techniques you can apply immediately to your own services.

Transcript

1. Oleg Nenashev CNCF Ambassador Modeling AWS service providers with Testcontainers, WireMock and Localstack
2. 2 Java All the Way Down Up Application Unit Tests Build Definition and Pipelines Integration Tests Infrastructure-as-Code Deployment Pipelines Deployment Tests Production Health Checks Java the stack up all the way
3. Today at 3 Localstack 1. If Needed: Tools Overviews and Integration Testing 2. Mocking and Modeling AWS services in integration tests 3. DYI developer environments with Spring Boot Dev Services 4. Infrastructure as Code (IaC) & Pulumi 5. Testing IaC locally & autotests 6. Advanced Troubleshooting
4. Async Q&A: Testcontainers Slack, WireMock Slack speakerdeck.com/onenashev
5. > whoami @oleg_nenashev oleg-nenashev Dr. Nenashev / Mr. Jenkins Developer Tools Hacker Community Builder DevRel Consultant #RussiansAgainstPutin #StandWithUkraine
6. Tell your story at KCD Suisse Romande! 04-05 December 2025 - kcd.cloud-native-romandy.ch CFP opens on July 1st
7. 7 Staging & QA Tests Build Integration tests Build Tests Gaining confidence in you software “Shift Left” with modern tools
8. About You
9. “Shift Left”, they said? YAML, they gave? 9
11. Our Repository github.com/oleg-nenashev/workshop-aws-mocks-as-code git clone it
12. Workshop Prerequisites • Java 21 & your favorite IDE • Testcontainers-compatible Docker environment ◦ Tested on: Docker Desktop ◦ You can (try?) use: Podman, Colima, Rancher Desktop (list) ◦ OR: Testcontainers Cloud • Pulumi CLI + registration ◦ Guide: www.pulumi.com/docs/install/ 12
13. Do you `make it`? IT - Integration Tests
17. Ways to do API integration testing 1. Testing against Production/Staging servers 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 Slow Fast Nope Accu- rate * For Testcontainers, see the slides
18. 18 https://martinfowler.com/articles/ mocksArentStubs.html
19. 19 Localstack www.localstack.cloud
20. LocalStack • Local AWS Services emulation OR mocking • “awslocal” CLI utility • SDKs for languages and test frameworks 20 docs.localstack.cloud
21. 21 x.com/dastbe/status/1303858170155081728
22. Some of Them 22 • Emulated: S3, SQS, … • Mocked: EC2 (in the FOSS lib) • Thoughts & Prayers: AWS GreenShift ;) • …
23. Demo github.com/oleg-nenashev/workshop-aws-mocks-as-code/tree/main/3 _localstack-application 23
25. 25 SDKs testcontainers.org … and
27. 27 LOCAL STACK LocalStack Module K3s Module
28. Our Application 28
29. 29 AWS S3 SQS External API Our Application
30. Spring Boot and Dev Services hdocs.spring.io/spring-boot/reference/features/dev-services.html
31. See: Presentation by Moritz Halbritter 31 https://www.youtube.com/watch?v=Yqss7tYP890
32. Demo Time 32 https://github.com/oleg-nenashev/workshop-aws- mocks-as-code/tree/main/2_api-mocking
33. 1. Add Testcontainers Test 33 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
34. 2. Init Localstack containers 34 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
35. 3. Configure the app to use the Mock service 35 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
36. 4. Write your first test! 36
37. No Implementation? 37 Fake it until you “$ make it”
38. Ways to do API integration testing 1. Testing against Production/Staging servers 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 Slow Fast Nope Accu- rate * For Testcontainers, see the slides
39. wiremock.org/docs/stubbing IF (request_url) THEN (response) * * it gets MUCH more complex WireMock Config JSON: Client library response request Client App Mock API Server HTTP/2 API Mocking 101
40. API Mocking Tools Main implementation in Java Native lib, Docker images and Testcontainers modules Support for GraalVM Rich Ecosystem Sandbox CNCF Project Golang / Microservice arch Docker image, Testcontainers module, All-in K8s Charts Less Rich Ecosystem
41. WireMock Ecosystem & Features wiremock.org/docs
42. WireMock Ecosystem wiremock.org/docs
43. WireMock Ecosystem / Java • Java • Kotlin • Scala • Groovy • Clojure • (?)Android 43 • JUnit 4/5 • Testcontainers • Sprint Boot • Spring Cloud Contract • Quarkus • Maven • Spock • Pact
44. Standalone WireMock in Java wiremock.org/docs/stubbing
45. 45 WireMock has an official Testcontainers module! testcontainers.com/modules/wiremock
46. Example - JUnit 5 46
47. Demo Time 47 github.com/oleg-nenashev/mocks-as-code-demo
48. 48 Infrastructure-as-Code, for real
50. 50 And more constructive!
51. HOWTO: JavaDev-Ops 51
52. Enter -as-Code Tools! • Infrastructure as Real Code • SDKs for programming languages • Standard IDEs • Standard Developer Tools • Extensibility via libraries 52
53. • Open-Ecosystem Tool for Infra-as-Code • Open Source SDKs 53
54. • Multiple destinations 54 www.pulumi.com
55. • 120+ extensions: www.pulumi.com/registry/ 55 www.pulumi.com
56. Pulumi for Java 56 pulumi.com/docs/languages-sdks/java/
57. build.gradle 57
58. 58 Java All the Way Down Up Application Unit Tests Build Definition and Pipelines Integration Tests Infrastructure-as-Code Deployment Pipelines Deployment Tests Production Health Checks Java the stack up all the way
59. 59 Localstack
60. Pulumi Local • github.com/localstack/pulumi-local • Setting the environment and the configuration right • Just a script 60 Localstack
63. Hacking Time! 63 github.com/oleg-nenashev/mocks-as-code-demo/ tree/main/3_deployment
64. Read More 64 • github.com/localstack-samples/samp le-gradle-pulumi-testcontainers/blo b/main/README.md by Nancy Chauhan and Anca Ghenade Localstack
66. Pulumi for AWS or AWS Native? • AWS Native configuration is not applied for endpoints • APIs are slightly different in the package 66
68. When it Goes wrong 68
72. 72 Java All the Way Down Up Application Unit Tests Build Definition and Pipelines Integration Tests Infrastructure-as-Code Deployment Pipelines Deployment Tests Production Health Checks Java the stack up all the way
73. Deployment Pipelines and Health Checks • There are tools for that, too! • Testcontainers modules for k3s and KIND • You can deploy your CI/CD tools there • Modern Java tools have wrappers, too ◦ E.g. Quarkus - docs.quarkiverse.io/quarkus-helm/dev/example-argocd • Health checks via OTel, AWS CloudWatch or CloudTrail ◦ CloudWatch is a free LocalStack plan, CloudTrail is not 73
74. References • Main Demo: github.com/oleg-nenashev/mocks-as-code-demo • This and other presentations: speakerdeck.com/onenashev/
75. Keep Learning Tools 75 * AKA: Burning Out 101
77. It’s [always] a great time to contribute! testcontainers.org/contributing wiremock.org/participate 77
78. What I’m looking forward to? • Feedback from Java developers • Is Infra-as-Code with Java interesting to you? • Do you want Pulumi-LocalStack for Java productization?
79. Credits 79 • Siva Prasad Reddy and Oleg Shelajev, Docker / ex AtomicJar • Nancy Chauhan and Anca Ghenade, ex LocalStack • The demos are based on: ◦ github.com/testcontainers/tc-guide-testing-aws-service-integrations-using-loca lstack ◦ github.com/testcontainers-community/testcontainers-wiremock-demo ◦ github.com/oleg-nenashev/spring_io_2025-Testcontainers-workshop
80. GitHub: oleg-nenashev Twitter: @oleg_nenashev Thank you! Any questions? Testcontainers Slack 80