When we talk about test cases, we mostly mean unit tests. It is incorrect to assume that the unit that we want to test is always a function. The unit (or unit of work) is a logical unit that constitutes a single behavior. This unit should be able to be invoked via a public interface and should be testable independently.
Thus, a unit test performs the following functions:
It tests a single logical function
It can be run without a specific order of execution
It takes care of its own dependencies and mock data
It always returns the same result for the same input
It should be self-explanatory, maintainable, and readable
Note
Martin Fowler advocates the test pyramid (http://martinfowler.com/bliki/TestPyramid.html) strategy to make sure that we have a high number of unit tests to ensure maximum code coverage. The test pyramid says that you should write many more low-level unit tests than higher level integration and UI tests.
There are two important testing strategies that we will discuss...