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 test 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/Gradle as examples, you'll see live coding that shows how these tools work together, though the approach applies 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 immediately apply to your own services.

Transcript

1. Oleg Nenashev Gradle Inc. / 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: Gradle Community Slack, Testcontainers Slack speakerdeck.com/onenashev
5. > whoami @oleg_nenashev oleg-nenashev Dr. Nenashev / Mr. Jenkins Developer Advocate, Gradle Developer Tools Hacker Community Builder #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 Developer Happiness and Productivity Engineering (DPE)
9. 9 Staging & QA Tests Build Integration tests Build Tests Gaining confidence in you software “Shift Left” with modern tools
10. About You app.sli.do/event/drRyzvmTGW KEaqu8eCgJHE
11. “Shift Left”, they said? YAML, they gave? 11
13. Our Repository github.com/oleg-nenashev/workshop-aws-mocks-as-code git clone it
14. 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/ • Nice2Have: Build Scan account ◦ scans.gradle.com/ 14
15. Do you `make it`? IT - Integration Tests
19. 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
20. 20 https://martinfowler.com/articles/ mocksArentStubs.html
21. 21 Localstack www.localstack.cloud
22. LocalStack • Local AWS Services emulation OR mocking • “awslocal” CLI utility • SDKs for languages and test frameworks 22 docs.localstack.cloud
23. 23 x.com/dastbe/status/1303858170155081728
24. Some of Them 24 • Emulated: S3, SQS, … • Mocked: EC2 (in the FOSS lib) • Thoughts & Prayers: AWS GreenShift ;) • …
25. Demo github.com/oleg-nenashev/workshop-aws-mocks-as-code/tree/main/3 _localstack-application 25
27. 27 SDKs testcontainers.org … and
28. Java Example 28 • There is a BOM for Testcontainers • Use platforms definitions for it (in Gradle) . . .
30. 30 LOCAL STACK LocalStack Module K3s Module
31. Our Application 31
32. 32 AWS S3 SQS External API Our Application
33. Spring Boot and Dev Services hdocs.spring.io/spring-boot/reference/features/dev-services.html
34. See: Presentation by Moritz Halbritter 34 https://www.youtube.com/watch?v=Yqss7tYP890
35. Demo Time 35 https://github.com/oleg-nenashev/workshop-aws- mocks-as-code/tree/main/2_api-mocking
36. 1. Add Testcontainers Test 36 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
37. 2. Init Localstack containers 37 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
38. 3. Configure the app to use the Mock service 38 https://github.com/oleg-nenashev/mocks-as-code-demo/blob/main/1_application/src/test/ java/com/testcontainers/demo/MessageListenerTest.java
39. 4. Write your first test! 39
40. No Implementation? 40 Fake it until you “$ make it”
41. 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
42. 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
43. 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
44. WireMock Ecosystem & Features wiremock.org/docs
45. WireMock Ecosystem wiremock.org/docs
46. WireMock Ecosystem / Java • Java • Kotlin • Scala • Groovy • Clojure • (?)Android 46 • JUnit 4/5 • Testcontainers • Sprint Boot • Spring Cloud Contract • Quarkus • Maven/Gradle • Spock • Pact
47. Standalone WireMock in Java wiremock.org/docs/stubbing
48. WireMock Plugin for Gradle 48 William-Hill-Online/wiremock-gradle-plugin
49. 49 WireMock has an official Testcontainers module! testcontainers.com/modules/wiremock
50. Example - JUnit 5 50
51. Demo Time 51 github.com/oleg-nenashev/mocks-as-code-demo
52. 52 Infrastructure-as-Code, for real
54. 54 And more constructive!
55. HOWTO: JavaDev-Ops 55
56. Enter -as-Code Tools! • Infrastructure as Real Code • SDKs for programming languages • Standard IDEs • Standard Developer Tools • Extensibility via libraries 56
57. • Open-Ecosystem Tool for Infra-as-Code • Open Source SDKs 57
58. • Multiple destinations 58 www.pulumi.com
59. • 120+ extensions: www.pulumi.com/registry/ 59 www.pulumi.com
60. Pulumi for Java 60 pulumi.com/docs/languages-sdks/java/
61. build.gradle 61
62. 62 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
63. 63 Localstack
64. Pulumi Local • github.com/localstack/pulumi-local • Setting the environment and the configuration right • Just a script 64 Localstack
67. Hacking Time! 67 github.com/oleg-nenashev/mocks-as-code-demo/ tree/main/3_deployment
68. Read More 68 • github.com/localstack-samples/samp le-gradle-pulumi-testcontainers/blo b/main/README.md by Nancy Chauhan and Anca Ghenade Localstack
70. Pulumi for AWS or AWS Native? • AWS Native configuration is not applied for endpoints • APIs are slightly different in the package 70
72. When it Goes wrong 72
77. Problems Report 77
78. 78 gradle --scan Gradle Profiler Java Tools and IDEs Gradle Observability
79. 79 OpenTelemetry plugin for Gradle • Injects traces and spans to the Gradle execution • Helps to find the slowest parts of your build with the Gradle OpenTelemetry build plugin. • Created by Craig Atkinson • craigatk/opentelemetry-gradle-plugin
81. 81 Gradle tasks tracing github.com/craigatk/ opentelemetry-gradle-plugin
82. Tests traces too! github.com/craigatk/opentelemetry-gradle-plugin 82
83. But Not Insights? 83
84. Based On True Events 84
85. Build Scan & Develocity 85
86. Demo Time 86 github.com/oleg-nenashev/mocks-as-code-demo
87. ◦ Build Scans and Troubleshooting ◦ Local and Distributed build caching ◦ Predictive Test Selection ◦ Flaky Tests Detection ◦ Local build observability ◦ // And more! gradle.com/develocity Apache Maven, Gradle Build Tool, sbt, Bazel + Python + NPM
88. • For many open source projects: Gradle sponsors Develocity licenses/hosting, helps with build optimization and developer productivity • Maven, Bazel and sbt projects welcome gradle/develocity-oss-projects
89. works for Pulumi and Integration Tests Tools! 89
91. 91 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
92. 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 92
93. 2025: Move to Kotlin? blog.gradle.org/kotlin-dsl-is-now-the-default -for-new-gradle-builds • 2023 - Kotlin is a default for Gradle build authoring • Scripts, Plugins, DSL extensions • One language to rule them all?
94. References • Main Demo: github.com/oleg-nenashev/mocks-as-code-demo • This and other presentations: speakerdeck.com/onenashev/ • Build Scan: scans.gradle.com • Develocity: https://gradle.com/develocity/
95. Keep Learning Tools 95 * AKA: Burning Out 101
97. It’s [always] a great time to contribute! community.gradle.org/contributing testcontainers.org/contributing wiremock.org/participate 97
98. 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? • Any other feedback on Gradle :)
99. Credits 99 • 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
100. GitHub: oleg-nenashev Twitter: @oleg_nenashev Gradle Community Slack, #developer-productivity-engineering Thank you! Any questions? Testcontainers Slack 100