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Service Virtualisaion

Installation (Gradle)

compile group: "org.http4k", name: "http4k-testing-servirtium", version: "3.248.0"

About

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:

  1. In a Recording contract - using a MiTM proxy which sits between the Client-Under-Test and 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 Date headers etc.
  2. In a Replaying contract - 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]:

  1. [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-Test utilises a http4k Client, since it leverages the Server-as-a-Function paradigm.

  2. 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.

  3. 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.

Kotlin Examples:

Java Examples: