by Horatiu Dan

As a product is being developed and maintained its test suite is enriched as features and functionalities are added and enhanced. Ideally, development teams should aim having a lot of quick unit tests that are run whenever modifications in the code are made. It is great if these are written before or at least together with the tested code, cover as many use cases as possible and finish running after a reasonable amount of time. By all means, a reasonable amount of time is an entity difficult to quantify.

On the other hand, there are a lot of live products that solve quite complex business problems whose thorough verification concerns cross-cutting through multiple application layers at once and thus, the number of integration tests is significant. Running all these unit and integration tests whenever the code is touched is not always feasible, as the productivity and the development speed is decreased considerably. Again, productiv...