The Three Mocketeers and d'AIrtagnan

When modeling (aka “mocking”) services during software development, you need to mimic APIs, databases, and other data providers. You can't do this with just one tool; you need to combine several. The good news is that the Testcontainer ecosystem makes it possible to do this with just a few lines of code! And it's available for many ecosystems: Java, Python, JavaScript, Golang, C/C++, .NET, etc.

In this session, I'll demonstrate some ways to create test services, databases, and API providers using Testcontainers and WireMock for a modern Java project, with Gradle and Quarkus. The same approach can be used for other languages, and I'll present examples for Python! Then, we'll extend the approach by adding fake data generation using the Faker or Synthesized libraries, which can be used for both relational and sequence data.

P.S.: And who is d'Artagnan? Prepare for a surprAIse!

Transcript

1. 1 The Three Mocketeers and d’AIrtagnan Oleg Nenashev Gradle, Inc.
3. Source: Holy Grail des Monty Python Attention Oleg va parler français!
4. > whoami @oleg_nenashev oleg-nenashev Dr. Nenashev / Mr. Jenkins Developer Advocate, Gradle Developer Tools Hacker Community Builder #RussiansAgainstPutin #StandWithUkraine
5. > whoami –suisse-romande Cloud Native Suisse Romande API Neuchâtel (RIP, Silicon Neuchalet?) Silicon Chalet Ambassador
6. Tell your story at KCD Suisse Romande 04-05 December 2025 - kcd.cloud-native-romandy.ch CFP is Open!
7. Les Trois “Moque-taires” - Tous comme un, un comme tous (sic!)
8. 8 The Three Mocketeers and d’AIrtagnan
9. Outline • Intro to API integration testing • Testcontainers and WireMock • Using them together • Faking data • Add some AI? :) 9
10. Async Q&A: Gradle Community Slack, Testcontainers and WireMock Slack speakerdeck.com/onenashev
11. What is your technology stack? 11
12. /me discussing this talk 12
14. 14 kotlinlang.org/docs/data-analysis-overview.html Kotlin for Data Science • Kotlin Notebook • Kotlin DataFrame • Kandy for visualization • Everything Java has to offer
15. Our Tools for today 15
16. 16 Developer Happiness & Productivity Engineering (DPE)
18. ◦ Build Scans and Troubleshooting ◦ Local and Distributed build caching ◦ Predictive Test Selection ◦ Flaky Tests Detection ◦ Local build observability ◦ // And more! https://gradle.com/develocity/ Apache Maven, Gradle Build Tool, sbt, Bazel + Python + NPM
19. You work on Data, right? 19
20. Source: https://kids-first.github.io/kf-airflow- dags/warehouse.html kidsfirstdrc.org 20
21. Source: https://kids-first.github.io/kf-airflow- dags/warehouse.html Data Provider APIs 21
22. APIs
23. 23 Source: https://pixelfriedhof.com/en/csv-is-not-an-interface/
24. Most of data comes from APIs • opendata.swiss • kidsfirstdrc.org/portal/portal-about-data • vs.inf.ethz.ch/res • github.com/public-apis/public-apis • www.kaggle.com/datasets • data.world 24
25. 25 Source: https://medium.com/10-minutes-qa-story/api-testing-from-scratch-api-anatomy-f220856ce9b3
27. Do you `make it`? IT - Integration Tests 27
29. Integration Testing 29 • Multiple technology stacks and toolchains • Many teams involved • Sacred knowledge • [Almost] always too late
31. 31 Do You Still Have A Test Environment?
32. 32 devcontainers Testcontainers Cloud IDEs Dev/Test Environments are no more?
33. Quarkus Dev Services • Automatic provisioning of unconfigured services in development and test mode • Transparent to your application • Mostly containerized, with Testcontainers 33 https://quarkus.io/guides/dev-services
34. 34 Build Unit tests Publish Reports Integration tests Publish Reports WAS
35. 35 Build Unit tests Publish Reports Integration tests Publish Reports NOW “Shift Left” Fast integrations tests are critical
36. Ways to do integration testing 1. Testing against Production/Staging servers 2. Testing against a simplified/containerized instance (e.g. Testcontainers) 3. Mocking at the API provider level (e.g. WireMock or Microcks) 4. Mocking at the code level 36 Slow Fast Nope Accu- rate
37. 37 Staging & QA Tests Build Integration tests Build Tests Gaining confidence in you software
39. Why containers? • Configuration Management • Fast provisioning • Clean environments • Disposability • Clustering
40. Docker • Popular container engine • Developer-friendly • Huge ecosystem • DockerHub and Container Registries • Docker Compose – multi-container apps • Universal image format (OCI) https://www.docker.com/
42. 42 SDKs C/C++ testcontainers.com
43. 43 testcontainers.com/modules
44. Testcontainers for Python 44 • Started by Sergey Pirogov, now - Till Hoffmann • github.com/testcontainers/testcontainers-python • testcontainers-python.readthedocs.io testcontainers.com
45. Containers are not always slow! • On-demand image build • Caching Docker image builds • Suspending containers between tests • Graceful termination ◦ github.com/testcontainers/moby-ryuk 45 testcontainers.com
46. * Testcontainers/AtomicJar is a WireMock partner 46
47. 47 WireMock has an official Testcontainers module! testcontainers.com/modules/wiremock
48. wiremock.org
49. 49 wiremock.org IF (request_url) THEN (response) * * it gets MUCH more complex WireMock Config JSON: Client library response request Client App Mock API Server HTTP/2
50. API Mocking for Java. Examples en.wikipedia.org/wiki/Comparison_of_API_simulation_tools Proprietary Open Source `
51. 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
52. WireMock in Java wiremock.org/docs/stubbing
53. WireMock Ecosystem & Features 53 wiremock.org/docs
54. WireMock Plugin for Gradle 54 William-Hill-Online/wiremock-gradle-plugin
55. WireMock Ecosystem & Features 55 wiremock.org/docs
56. Example - JUnit 5 56
57. 57 WireMock Standalone client from wiremock.constants import Config from wiremock.client import * Config.base_url = 'https://mockserver.example.com/__admin/' mapping = Mapping( priority= 100, request=MappingRequest( method=HttpMethods.GET, url= '/hello' ), response=MappingResponse( status= 200, body= 'hi' ), persistent= False, ) mapping = Mappings.create_mapping(mapping=mapping) all_mappings = Mappings.retrieve_all_mappings() More: github.com/wiremock/python-wiremock Client library response request Test Mock API Server HTTP/2
59. WireMock as a Proxy 59 Tests Real API Provider OR • Recording • Fault injection • Protocol Verification
60. WireMock Record & Playback wiremock.org/docs/record-playback • Record communications • Capture data • Replay the requests • Reverse-engineer protocols to OpenAPI 60
61. WireMock Faker Extension github.com/wiremock/wiremock-faker-extension • There’re many Data::Faker library ports ◦ Python: joke2k/faker ◦ Ruby: faker-ruby/faker (logo source!) ◦ Java: datafaker-net/datafaker • We use the Java one • It can be included in a Testcontainer image 61
62. WireMock Faker Extension wiremock.org/docs/response-templating/#fake-data-helpers 62 "response": { "status": 200, "jsonBody": { "namme": {{random 'Name.first_name'}} "surname": {{random 'Name.last_name'}} "postcode": {{random 'Address.postcode_by_state.AL' }} } }
63. Simple data is not enough? 63 www.synthesized.io
64. Synthesized’ Data offerings 64 Synthesized Scientific Data Kit (SDK) Synthesized Test Data Kit (TDK) Synthesized Fairlens (Data Bias) www.synthesized.io Data sets / Streams *.CSV Relational datasets (for databases)
65. 65 Testcontainers Module for Synthesized TDK • Only TDK - Relational Data • Only Java Module No Runtime Use at the moment, But NOT a showstopper
66. 66 TDK SDK Database Module for Testcontainers App Tests WireMock Module Build On-Demand Your App Tests • Random Fetch • CSV => JSON generator
68. github.com/wiremock/wiremock-docker/ tree/main/samples/random 68
69. And d'AIrtagnan 69
70. 70 * bad idea
71. When AI in tests? • Non-structured text • Not enough test data • Exploratory Testing & Prototyping • Testing GenAI/Model Integrations themselves 71 WHEN ENGINEERS MENTION AI-GENERATED DATA
73. 73 https://mokksy.dev/
74. AI Providers can be modeled, too 74 1. Testcontainers and WireMock ◦ OpenAI has an OpenAPI specification ◦ https://github.com/openai/openai-openapi 2. Local Models ◦ Ollama ◦ Langchain4j ◦ Docker Model Runner Recommended
75. Using Local Models > ollama run qwen3:1.7b > ollama run devstral:24b - For Coding > docker model run ai/gemma3-qat:1B-Q4_K_M 75
76. 76 https://quarkus.io/blog/quarkus-meets-langchain4j/
77. When to Mock LLM models? • Reproducible Behavior • Fault/Latency Injection • Proxying and Recording behavior • Mocking MCP Services 77
78. Demo Homework: • https://quarkus.io/quarkus-workshop-langchain4j/ • github.com/quarkusio/quarkus-workshop-langchain4j Now: https://github.com/quarkiverse/quarkus-langchain4j/tree/main/samples https://github.com/langchain4j/langchain4j-examples 78
79. 79 https://quarkus.io/blog/agentic-ai-with-quarkus/ Model https://docs.quarkivers e.io/quarkus-langchain 4j/dev/ollama.html
80. Model Context Protocol (MCP) 80 modelcontextprotocol.io
81. Model Context Protocol (MCP) • APIs, but also for your Models / AI Pipelines • Based on JSON-RPC 2.0 • Can be and must be tested • Same tools 81 modelcontextprotocol.io
82. Interface is simple… but may be asynchronous 82 modelcontextprotocol.io
83. Example - MCP PoC for Gradle Daemon 83 github.com/IlyaGulya/gradle-mcp-server
84. How does one test it? 84
86. 86 Beware of… • Frameworkitis • Flaky tests • Too many tests • Parallelization & resource optimization • Lack of observability * Saw (2004) Yes, that elephant in the room
87. ◦ Build Scans and Troubleshooting ◦ Local and Distributed build caching ◦ Predictive Test Selection ◦ Flaky Tests Detection ◦ Local build observability ◦ // And more! https://gradle.com/develocity/ Apache Maven, Gradle Build Tool, sbt, Bazel + Python + NPM
89. Takeaways 89 • Shift left your integration testing • Mock APIs and Data • There are tools for that, including WireMock and Testcontainers • Model your AI services and LLMs
90. Choosing a right foundation tool for ITs • 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 90 * Your mileage may vary ** More later *** I just like footnotes * Likely, you want to use both
91. Demos from today • github.com/wiremock/wiremock-docker • github.com/wiremock/wiremock-docker/tree/main/samples/random • github.com/oleg-nenashev/gradle-quarkus-plugin-demo • github.com/ollama/ollama • github.com/quarkusio/quarkus-workshop-langchain4j • github.com/quarkiverse/quarkus-langchain4j/tree/main/samples 91
93. It’s [always] a great time to contribute! community.gradle.org/contributing testcontainers.org/contributing wiremock.org/participate 93
94. GitHub: oleg-nenashev Twitter: @oleg_nenashev Gradle Community Slack, #developer-productivity-engineering Questions? Testcontainers Slack 94
95. Credits to • All WireMock contributors • WireMock Inc. Team • All Testcontainers contributors and AtomicJar folks • All FOSS contributors 95