fix: rephrase software coverage for clarity

chapters/software-tests.md

 
 ## Software Tests
 
-All functions (except getter and setter methods) `MUST` provide proper tests.
-This is understood on a component level, meaning every method should have at least one test.
-Whether you achieve this by Test Driven Development (TDD) or other means depends on your preferred way to work.
+Software tests aim at ensuring that the code you write does exactly what you expect it to do.
+
+All functions (except `get`ter and `set`ter methods) `MUST` provide proper tests.
+Every method should have enough tests to cover each line of code, aiming at a code coverage of 100\%.
+Also all possible outcomes of a method should be considered and covered by tests.
 
-Please keep in mind not only to write a test for each of your functions but also
-consider all possible outcomes.
-It is e.g. not sufficient to test if a function creates a file if the written content depends on variables etc.
+Whether you achieve this by Test Driven Development (TDD) or other means depends on your preferred way to work.
 
 Examples for writing tests in different programming languages are: