Our unit tests are written using the [catch2 framework](https://github.com/catchorg/Catch2/blob/devel/docs/assertions.md)
In catch2 we prefer the ```CHECK``` family of macros since they will continue the test in case of failure, while the ```REQUIRE``` family would terminate.
In catch2, testing is particularly easy. For details, see the catch2 documentation above, but in short: ```CHECK( expression );``` where expression evaluates to a boolean, is just enough.
- For all code we want to test all interfaces and basic functionality.
- see also the "coverage", which indicates the number of actual code lines that are tested by unit tests. We want this to converge to 100%.
- Unit tests should be robust and run very fast.
- no extensive physics tests
- no statistical analysis with large number of events
- if needed, complicated input-output data/objects must be replaced with simplified (empty) testing counterparts to basically **only** test the basic expectations, not complex behavior.
- unit tests must be as independent of each other as possible. Ideally they only depend on exactly the code they are testing.
