Microservices Testing: Key Strategies and Tools
In this post, we'll learn the importance of different types of testing, from unit testing to contract testing, and the tools to help including Pact, Vercel, and more.
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Development teams are increasingly choosing a microservices architecture over monolithic structures in order to boost apps' agility, scalability, and maintainability. With this decision to switch to the modular software architecture — in which each service is a separate unit with its own logic and database that communicates with other units through APIs — comes the need for new testing strategies and new testing tools.
Testing microservices is a critical part of the microservices application process: you need to ensure that your code doesn’t break within the unit, that the dependencies in the microservices continue to work (and work quickly), and that your APIs meet the defined contracts. Yet, because many microservices are built with a continuous delivery mode to build and deploy features consistently, developers and DevOps teams need accurate and reliable testing strategies to be confident in these features.
So which different types of tests exist for microservices, how can they work for other areas of your software, and what are their benefits? The well-known "testing pyramid" can provide a testing framework for approaching these tests.
According to Martin Fowler, a prominent author on software engineering principles, “The 'Test Pyramid’ is a metaphor to group software tests into buckets of different granularity.”
The different layers of the pyramid are defined as:
- Unit tests: Test a small part of a service, such as a class.
- Component tests: Verify the behavior of individual services.
- Integration tests: Verify that a service can interact with infrastructure services, such as databases and other application services, by testing the service’s adapters.
Note: some versions of the testing pyramid switch the order of component tests and integration tests.
- End-to-end tests: verify the behavior of the entire application.
Combining multiple microservices testing strategies leads to high test coverage and confidence in your software while also making overall maintenance more manageable.
Unit testing aims to ensure that the smallest portion of service performs as expected, within the specification that has been decided upon during the microservices design phase. Because microservices break down application functionality into hundreds of small testable functionality components, unit testing treats each one individually and independently. It’s best practice to unit test on the level of a class or that of a group of related classes.
Unit testing can cut off a component’s dependencies by using test doubles such as fakes, stubs, mocks, dummies, and spies. For example, testers can mock the responses for your dependencies and "assume they do [X]" where [X] is the correct response, a failure response, etc.
Component testing verifies that a given service is functioning correctly. With the scope limited to a portion of the entire microservices architecture, component testing checks the end-to-end functionality of a chosen microservice (which can be made up of a few classes) by isolating the service within the system, replacing its dependencies with test doubles and/or mock services.
You can create test environments for each component that will be divided into test cases. It might involve testing resource behavior, for example, such as performance testing, determining memory leaks, structural testing, etc.
Integration testing validates that independently developed components/microservices work correctly when they are connected. It tests the communication paths and interactions between components and finds errors.
Integration tests become more difficult and time-consuming to write and run. Therefore, having excellent production QA (Quality Assurance) practices will help ensure this goes smoothly.
It’s crucial to call out contract testing in the testing pyramid. Contact testing checks the compatibility of separate units (like two microservices), by making sure they can communicate with each other. Contract testing tests that APIs work, which is the way that microservices interact with each other.
Contract testing checks these microservices’ boundaries and interactions and stores them in a contract, which can then be used as a standard for how both parties interact in the future. It requires both parties to agree on the allowed set of interactions and allows for evolution over time.
End-to-end testing (E2E testing) is the final testing stage that involves testing an application's workflow from beginning to end for complete user journeys.
These tests can be automated, but E2E testing is only done for ultra-critical flows. It doesn’t scale well in a microservices architecture since it requires you to spin up many microservices and wire them up, which is challenging to automate and maintain. As a result, it’s reserved for testing only critical interactions between specific microservices.
Microservices Testing Tools To Use, Including On-Demand Staging Environments
Developers and QA teams have different preferences for microservices testing tools, especially for these different types of tests. Here’s a rundown of some popular ones. Many are on-demand staging environments, which are created dynamically, triggered by a CI/CD pipeline. With on-demand staging, once a developer is done with the staging environment, the staging environment is destroyed, along with any configuration, environment, or installation inconsistency.
WebApp.io (Formerly LayerCI)
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