Adding or removing tests is a little bit cumbersome currently: the test
needs to be added to CMakeLists.txt, the init function needs to be
predeclared in pybind11_tests.cpp, then called in the plugin
initialization. While this isn't a big deal for tests that are being
committed, it's more of a hassle when working on some new feature or
test code for which I temporarily only care about building and linking
the test being worked on rather than the entire test suite.
This commit changes tests to self-register their initialization by
having each test initialize a local object (which stores the
initialization function in a static variable). This makes changing the
set of tests being build easy: one only needs to add or comment out
test names in tests/CMakeLists.txt.
A couple other minor changes that go along with this:
- test_eigen.cpp is now included in the test list, then removed if eigen
isn't available. This lets you disable the eigen tests by commenting
it out, just like all the other tests, but keeps the build working
without eigen eigen isn't available. (Also, if it's commented out, we
don't even bother looking for and reporting the building with/without
eigen status message).
- pytest is now invoked with all the built test names (with .cpp changed
to .py) so that it doesn't try to run tests that weren't built.
The C++ part of the test code is modified to achieve this. As a result,
this kind of test:
```python
with capture:
kw_func1(5, y=10)
assert capture == "kw_func(x=5, y=10)"
```
can be replaced with a simple:
`assert kw_func1(5, y=10) == "x=5, y=10"`
Use simple asserts and pytest's powerful introspection to make testing
simpler. This merges the old .py/.ref file pairs into simple .py files
where the expected values are right next to the code being tested.
This commit does not touch the C++ part of the code and replicates the
Python tests exactly like the old .ref-file-based approach.
