Contract Testing using Pact
Overview
This article explains about contract testing and its importance and how we can test contract using Pact Net in dotnet core.
Contract Testing
Contract testing is a testing paradigm that focuses on the interactions between different services or components in a distributed system. The goal of contract testing is to ensure that each service can interact with others as expected, according to a predefined contract. These contracts define the expectations of how services communicate with each other, specifying details such as request and response formats, data types, and protocols.
Test Pyramid with Contract
Consumer and Provider
- Consumer: An application that makes use of the functionality or data from another application to do its job. For applications that use HTTP, the consumer is always the application that initiates the HTTP request (eg. the web front end), regardless of the direction of data flow. For applications that use queues, the consumer is the application that reads the message from the queue.
- Provider: An application (often called a service) that provides functionality or data for other applications to use, often via an API. For applications that use HTTP, the provider is the application that returns the response. For applications that use queues, the provider (also called producer) is the application that writes the messages to the queue.
Contract
- A contract defines the expected interactions between a consumer and a provider. It includes details such as the expected request format, response format, and any specific conditions or constraints.
Benefits
- Early Detection of Issues: Contract testing allows the early detection of issues in the interactions between services, preventing problems from propagating through the system.
- Isolation of Changes: Services can evolve independently as long as they adhere to the agreed-upon contracts. This enables more flexibility in making changes without affecting other services.
- Improved Collaboration: Consumer and provider teams can work more independently, and contract testing provides a shared understanding of the expected behavior.
Tools
- Pact: Pact is a popular contract testing tool that supports multiple programming languages and platforms. It allows you to define, generate, and verify contracts.
- Spring Cloud Contract: A contract testing library for Java-based applications, integrated with the Spring ecosystem.
- Consumer-Driven Contracts (CDC): The concept of consumer-driven contracts emphasizes that consumers define the contracts, and providers ensure compliance.
In this article, we will learn about only pact tool.
Pact
Pact is a open source and consumer driven testing framework that helps you implement contract tests between APIs. The benefit of this is you get fast feedback on any breaking changes that may occur when contracts change between APIs. This tool helps to test microservices quickly and independently.
A contract between a consumer and provider is called a pact. Each pact is a collection of interactions. Following is the interaction description for http and for messages:
For HTTP:
- An expected request — describing what the consumer is expected to send to the provider
- A minimal expected response — describing the parts of the response the consumer wants the provider to return.
For messages:
- The minimal expected message — describing the parts of the message that the consumer wants to use.
In this article we will cover only HTTP request and response.
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