Reasons for testing include, on the one hand, the risk that problems are only noticed in production and, on the other hand, that tests serve as an exact specification of the system (section 10.1).

Section 10.2 illustrated how using the concept of the test pyramid tests should be structured: The focus should be on fast, easily automatable unit tests. They address the risk that there are errors in the logic. Integration tests and UI tests then only ensure the integration of the microservices with each other and the correct integration of the microservices into the UI.

As section 10.3 showed, microservices can additionally deal with the risk of errors in production in a different manner: microservice Deployments are faster, they influence only a small part of the system, and microservices can even run blindly in production. Therefore the risk of Deployment decreases. Thus it can be sensible instead of comprehensive tests to rather optimize the Deployment in production to such an extent that it is, for all practical purposes, free of risk. In addition, the section discussed that there are two types of test pyramids for microservice-based systems: one per microservice and one for the overall system.

Testing the overall system entails the problem that each change to a microservice necessitates a run through this test. Therefore, this test can turn into a bottleneck and should be very fast. Thus, when testing microservices, one objective is to reduce the number of integration tests across all microservices (section 10.4).

When replacing legacy applications not only their functionality has to be transferred into microservices, but also the tests for the functionalities have to be moved into the tests of the microservices (section 10.5). Besides, each modification to a microservice has to be tested in the integration with the version of the legacy application used in production. The legacy application normally has a much slower release cycle than the microservices. Therefore, the version of the legacy application that is at the time in development has to be tested together with the microservices.

For testing individual microservices the other microservices have to be replaced by stubs. This enables you to uncouple the tests of the individual microservices from each other. Section 10.6 introduced a number of concrete technologies for creating stubs.

In section 10.7 client-driven contract tests were presented. With this approach the contracts between the microservices get explicit. This enables a microservice to check whether it fulfills the requirements of the other microservices—without the need for an integration test. Also for this area a number of tool are available.

Finally, section 10.8 demonstrated that technical requirements to the microservices can likewise be tested in an automated manner. This enables unambiguous establishment of whether a microservice fulfills all technical standards.

Essential Points

  • • Established best practices like the test pyramid are also sensible for microservices.
  • • Common tests across all microservices can turn into a bottleneck and therefore should be reduced, for example, by performing more consumer-driven contract tests.
  • • With suitable tools stubs can be created from microservices.
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