Top Contract Testing Tools Every Developer Should Know in 2024

What is Contract Testing?

In software development, complex systems are often built from interacting components. Contract testing establishes a well-defined interface, similar to an API, that governs communication between these components. This interface specifies the expected behavior of each component, including:

• Data formats: The structure and validation rules for data exchanged between components.

• Message specifications: The format and content of messages used for communication.

• Error handling: How errors and exceptions should be communicated and managed.

By defining and enforcing these contracts, contract testing ensures that components can interact seamlessly, regardless of their internal implementation details. This promotes:

• loose coupling, reduces integration complexity, and facilitates independent development and deployment of components.

  
  

What is consumer-driven contract testing?

Consumer-Driven Contract Testing is the widely accepted approach of performing contract testing.

Basically there are two parties involved in a contract, one asking for the data(consumer) and the other one providing the data(provider).

Here, the consumer of the service dictates the terms of the contract. It tells the provider what it expects in terms of data format and structure. The provider then ensures that it can meet these expectations.

This approach has several benefits:

1. Flexibility:

   Consumers define their requirements, leading to more flexibility and less risk of miscommunication.

2. Independence:

   Teams can work independently on their services, as long as they adhere to the agreed contracts.

3. Reduced Risk of Breakdowns:

   By ensuring that the provider meets the consumer's expectations, the risk of breakdowns in communication between services is significantly reduced.

How Does Contract Testing Work?

➡️ Defining the Contract: This is the core of Contract Testing.

A contract is a detailed agreement on how two services will interact. It includes the expected requests and responses, specifying the data format, structure, and types of fields.

For example, a contract might state that a request must include a customer ID as an integer and the response must include a status message.

➡️ Creating Contract Tests:

Once the contract is defined, each service involved writes tests to verify they can meet their part of the contract.

For the 'consumer' service (the one making requests), tests check if it sends requests correctly as per the contract. For the 'provider' service (the one responding to requests), tests ensure it can handle incoming requests and provide responses that match the contract.

The Process in Practice

Let's consider a practical example involving two services: a 'User Service' and an 'Order Service' in an e-commerce platform.

Step 1: Contract Creation

1️⃣ The teams responsible for the User Service and the Order Service come together to define the contract.

2️⃣ They agree that when the Order Service requests user details, it will send a user ID, and the User Service will respond with the user's name and address.

Step 2: Implementing Contract Tests

1️⃣ The Order Service team writes tests to ensure their service sends the correct request format with a valid user ID.

2️⃣ The User Service team writes tests to verify their service can handle these requests and respond with the correct user information.

Step 3: Continuous Testing and Integration

1️⃣ As development progresses, these tests are run frequently.

2️⃣If the User Service team changes their API and the response no longer matches the contract, the tests for the Order Service will fail. This signals a breach in the contract, alerting teams to resolve the issue.

Step 4: Versioning and Evolution

1️⃣ Contracts can evolve. When a service needs to change its API, it must also update the contract.

2️⃣ This ensures ongoing communication and agreement between teams, preventing unexpected failures in production due to mismatched expectations.

What are the Benefits of Contract Testing?

1. Problems are caught during development, not after deployment.

2. Teams can work on their services without constant coordination, as long as they adhere to the contracts.

3. Ensures that as long as the contract is respected, services will interact seamlessly in production.

4. Contract testing streamlines the integration and examination of microservices, making the process smoother.

5. The upkeep of the system is simplified and becomes less burdensome.

6. Contract testing allows for focused attention on individual modules. For instance, to assess module A's contract, there's no need for full integration with other modules; it can be evaluated on its own.

Contract Testing Use Cases

Contract testing stands out as an effective technique for verifying the dependability and interoperability of microservices and APIs. Nonetheless, it's important to note that it doesn't suit every testing need. Below, we outline several typical scenarios where contract testing is particularly beneficial:

Use Case 1: User Authentication in a Social Media App

➡️ Scenario:

In a social media application, there are two microservices: User Service and Post Service. The User Service handles user authentication, while the Post Service manages the creation and display of posts.

➡️ Contract:

The contract specifies that when the Post Service receives a user ID, it sends a request to the User Service to authenticate the user and receive basic user profile data.

Example Contract (JSON format):

{
  "request": {
    "path": "/authenticateUser",
    "method": "POST",
    "body": {
      "userId": "string"
    }
  },
  "response": {
    "status": 200,
    "body": {
      "userId": "string",
      "userName": "string",
      "isAuthenticated": "boolean"
    }
  }
}

➡️ Testing the Contract:

User Service: Tests to ensure it can process the authentication request and return user data in the correct format.

Post Service: Tests to verify it sends the correct user ID format and handles the received user data appropriately.

Understanding this use case, we can say that contract testing ensures that the microservices can reliably communicate with each other, adhering to the predefined contracts, which is vital for the smooth functioning of complex, distributed systems.

API Contract Testing Tools in 2024

API Contract Testing Tools are essential in modern software development, especially when dealing with microservices architectures. These tools help ensure that APIs behave as expected and adhere to their defined contracts.

We have covered both the free tools and the paid tools in the API Contract Testing category. The top 4 best performing API Contract Testing Tools to consider for 2024 are:

1. HyperTest

2. PACT

3. Spring Cloud Contract

4. Dredd

   
   

1. HyperTest - API Contract Testing Tool

HyperTest is a modern tool specifically designed for API contract testing. It offers robust capabilities for ensuring that APIs meet their specified contracts.

Key Features:

Request Tracking and Structure: HyperTest integrates as an SDK within each backend service. This allows it to intercept and record all incoming and outgoing requests, including their parameters, headers, and responses.

Test Generation: Based on the recorded requests, HyperTest constructs test cases. It analyzes the request flow, dependencies, and data to create a comprehensive test suite.

Test Coverage: HyperTest calculates code coverage to identify areas of the codebase that are adequately tested. It provides detailed reports on which code paths are covered by the generated tests.

Test Execution and Comparison: During test execution, HyperTest replays the recorded requests along with the mocked responses of any third-party calls and compares the responses with the original ones. Any discrepancies in structure or values indicate potential regressions.

Asynchronous Flow Testing: HyperTest can handle asynchronous flows, including messaging systems like RabbitMQ. It tracks message production and consumption, ensuring proper data flow and processing.

Database Testing: It can verify database calls, checking for correct data and queries before and after changes. This helps identify potential data integrity issues.

2. Pact - API Contract Testing Tool

Pact is a popular open-source tool for contract testing. It focuses on the interactions between consumer and provider by defining and verifying HTTP requests and responses.

Key Features:

Consumer-Driven Contracts: Pact allows the consumer to define the expected behavior of the provider, which can then be verified by the provider.

Mock Service: It provides a mock service for the consumer to interact with during testing, ensuring that the consumer's requests match the contract.

Integration with CI/CD: Pact integrates seamlessly with continuous integration/continuous deployment pipelines, enhancing the development workflow.

Language Support: Offers wide language support including Ruby, JVM languages (Java, Kotlin, Scala), .NET, JavaScript, Swift, and more.

3. Spring Cloud Contract - API Contract Testing Tool

Designed for Spring applications, this tool is used for implementing Consumer-Driven Contract (CDC) testing.

Key Features:

Integration with Spring: Perfect for applications built with the Spring framework.

Stub Runner: Automatically generates stubs for the consumer, which can be used for tests.

Supports Messaging: Apart from HTTP, it also supports contract testing for asynchronous messaging.

4. Dredd - API Contract Testing Tool

Dredd is a language-agnostic HTTP API testing tool that validates whether an API implementation adheres to its documentation.

Key Features:

Support for API Blueprint and OpenAPI: Works with API Blueprint and OpenAPI specifications.

Hooks: Offers hooks in several languages to set up preconditions or clean up after tests.

Continuous Integration: Easy integration with CI tools and services.

Conclusion

Each of these tools has its strengths and fits different needs in the API development lifecycle. The choice of tool often depends on the specific requirements of the project, such as the programming language used, integration capabilities, and the complexity of the API interactions. By employing these tools effectively, teams can ensure more reliable and robust API communication within their applications.

Here is a detailed comparison chart of the most widely used contract testing tools, click here to get to know those tools more technically.

Check out our other contract testing resources for a smooth adoption of this highly agile and proactive practice in your development flow:

• Tailored Approach To Test Microservices

• Comparing Pact Contract Testing And Hypertest

• Checklist For Implementing Contract Testing