Add more content about tests type

[JBonifay]

For the section of tests types definition (unit test, integration test, acceptance test…),
We may put the variants of definitions, speak about Inside-Out Outside-In, Classicist Mockist, London Chicago, sociable vs solitary, state-based vs interaction-based testing

[ ] Test types: unit test, integration test, acceptance test
[ ] Unit test types: sociable vs solitary
[ ] Testing types: state-based vs interaction-based testing
[ ] Directions: Inside-Out vs Outside-In
[ ] Schools: Classicist Mockist vs London Chicago