compile group: "org.http4k", name: "http4k-testing-servirtium", version: "3.241.0"
Service Virtualisation testing technology provides a way of declaring contracts which can record HTTP conversations to a custom Markdown format and then replaying them later offline. http4k provides a fully featured implementation of the Servirtium solution to implement this concept.
The basic idea is that you define an abstract contract Class/Interface which describes the expected behaviour for a system using a Client class (aka the
Client-Under-Test). This contract is then implemented twice:
- In a
Recordingcontract - using a MiTM proxy which sits between the
Client-Under-Testand the real service. This proxy records the HTTP traffic to a custom Markdown format which can be stored in a VCS, and can be configured to remove the dynamic sections of the traffic such as
- In a
Replayingcontract - using an MiTM server which matches incoming traffic and replays a recorded conversation for the matched requests in order from the Markdown file.
The result of these 2 implementations is that we can exercise the
Client-Under-Test code against different versions of the contract without performing any actual remote calls to prove compatibility. This is important because there may be complicated orchestration required for testing against a real system, or the end service may be unavailable or flaky.
http4k provides a few different pieces of support for [Serviritum]:
[JUnit5] extensions which provide the record/replay behaviour, providing a way to record and replay contracts without the use of a real server. This is only compatible when the
Client-Under-Testutilises a http4k Client, since it leverages the Server-as-a-Function paradigm.
MiTM proxy servers for record/replay behaviour, by inserting themselves as a proxy in the HTTP call chain and intercepting the HTTP traffic. This is compatible with HTTP clients using any JVM technology, not just http4k services - so can be used as a general JVM-based solution for implementing Servirtium-style tests.
A Storage Provider abstraction for storing and loading recorded contracts from various locations including disk and directly from GitHub.
Examples of use
Climate API Demo: github.com/http4k/servirtium-demo-kotlin-climate-tck. The climate API tested uses a simple programatic wrapper for World Bank's climate-data service. It can respond to requests with XML or JSON payloads, and the
http4k-testing-servirtium module can record and payback either. This is a standard showcase for Servirtium.
- Playback of a Servirtium recording: kotlin/DiskPlaybackClimateApiTests.kt
- Making a Servirtium recording: kotlin/DiskRecordingClimateApiTest.kt
- In the same package, see also a direct example for contrast, and one that can playback from recordings themselves on a website rather than from local disk.