Automation strategies for legacy systems

Wikipedia: A legacy system is an old method, old technology, old computer system or application that "belongs to or is related to a previous, outdated computer system" but is still in use.Often, referring to a system as a "legacy system" means that it may be outdated or in need of replacement.

What kind of system is a legacy system

Martin Fowler said Let's face it, all we are doing is writing tomorrow's legacy software today. This statement speaks to the harsh reality that every line of code our team writes now ends up being code for legacy systems.The disguised description shows that every R&D engineer is inseparable from the fate of transforming legacy systems.From Martin Fowler's description of legacy systems, we can easily see that legacy systems are not only measured by the time between the first line of code and the current time, but also include code quality, architectural design, DevOps pipelines, support systems, etc..The code quality of many legacy systems is very poor, and there are no automated quality assurance activities such as unit testing, API automated testing, and UI automated testing; the architectural design is chaotic, and various design methods and technologies are intertwined; there is no delivery pipeline, and all delivery processes areRelying on a few R&D engineers and other issues is the pain point that legacy systems need to face.

Michael Feathers defines a legacy system in his book Morking Bfectively with Legacy Code: A system without automated tests is a legacy system.Although this definition is not shared by everyone, it is enough to see that a legacy system without automated testing is a disaster for the development engineers involved in the modification.So for a legacy system, it is not always possible to start the refactoring method to complete the improvement of the project. It is also a good way to solve the pain points of legacy system changes by making up for automated testing.

How a legacy system without automated tests can make up for it

The overriding principle of legacy systems complementing automated testing practices is "let the automation test the code you change".This sentence guides all of us