What is Microservices Mocking? A Quick Intro

Microservices mocking is a a technique for replicating particular behaviors of real microservices in a controlled environment. Essentially, it's a practice of creating 'dummy' service operations to assess communication pathways and interactions between microservices. It comes into play where testing individual microservices independently could be convoluted due to dependencies on other services.

Mocking microservices allows for parallel development. Separate application teams can work concurrently, using mock APIs to simulate the response from microservices which aren't ready. This can significantly accelerate the development cycle. It also helps to circumvent unnecessary dependencies on third-party services or microservices that are a work in progress. It allows functionalities dependent on these services to proceed with the development and testing, without hindrances, inconsistencies, or potential cost implications.

When Would You Mocking for Microservices?

Microservices, as we know, have revolutionized the way developers compile and manage complex applications, using a suite of small services–each executing unique processes and communicating through simple mechanisms. In this framework, Microservices mocking is an essential tool for testing and design, in scenarios such as:

• Parallel development: During concurrent development, mocking microservices can help teams move faster. For instance, suppose a team is creating an Identity service handling user credentials and auth tokens. While this microservice is in progress, a mock version can be used by other teams that rely on this service. They can proceed with their tasks without delays, thus ensuring the overall project stays on schedule.
• Services dependent on third parties: There could be scenarios where your microservices are dependent on third-party APIs or services. Frequent calling of these services might be cost-prohibitive, result in unnecessary data usage, or even breach the terms of service. In such scenarios, mocking the third-party-dependent microservices serves the benefit of limitless and free testing and development, and prevents over-reliance on the third-party services.
• Unstable or unavailable microservices: When dealing with microservices that are either unstable due to ongoing development or frequently unavailable due to various reasons, having mock equivalents can result in a smoother development process. This both prevents wasted time waiting for the actual service and avoids the potential risk of testing with an unstable microservice.
• Testing and continuous integration: Microservices mocking can be crucial during the phases of testing and continuous integration. It allows development teams to carry out exhaustive unit tests, integration tests and end-to-end tests by simulating different scenarios, behaviors and responses. This, in turn, will help identify issues, bugs, or inefficiencies in the software, thus ensuring robustness of the system. Mocking also helps in automated testing as it enables the creation of reliable test conditions that are easily reproducible. Moreover, with mocked microservices, you can mitigate the risk of tests getting affected by external system failures, thus maintaining consistency in continuous integration and delivery pipeline.

Steps to Take When Mocking a Microservice

To understand better how to mock microservices, we will sketch out an example. Assume an application that involves a User Management Microservice, which is still in development. This Microservice is supposed to handle user authentication and returning user details.

1. Define microservices interactions and interfaces: Identify and define the interactions and interfaces that the actual microservice is expected to have. For the User Management Microservice, an endpoint such as /api/users with a GET method might be used. This endpoint would return user details.
2. Identify request parameters: Consider identifying any request parameters that your actual microservice would expect. The User Management Microservice, for instance, would require a userId parameter to return the right user details.
3. Define responses: Determine what the responses will look like; including the status codes, headers, and response bodies. A successful response from the User Management Microservice could return a 200 OK status code, standard headers, and a response body containing an object with user details.
4. Create mock microservices: You can use tools like WireMock Cloud to set up your mock microservice based on the details identified in the previous steps. WireMock allows you to setup a mock server that will engage with incoming requests and render similar responses as the actual microservice would.
5. Validate against real responses: Once set up, you can use this mock microservice for development and testing. Validate if it works correctly and responds as expected. Make necessary refinements and updates as needed. As you progress and as the actual microservices evolve, the mock version can mirror those changes,. Remember, it's crucial to keep an alignment between the mock versions and the actual microservices to have a reliable testing and development environment.