Missing and failing C++ tests

[ahoenselaar]

The current check testsuite only runs 22 C++ tests (20 when MPI is enabled) because eight tests are missing from the TESTS Automake variable:
https://github.com/NanoComp/meep/blob/master/tests/Makefile.am#L113

Out of the eight missing tests, four are failing at HEAD in a double-precision build:

• array-metadata
• dft-fields
• gdsII-3d
• ring-ll

In addition, absorber-1d-ll fails in single-precision builds.

[oskooi]

For reference, see #1878 which adds one of these missing tests (ring-ll.cpp) to the C++ make check suite. As I mention in #1878, there is probably no need to include every single missing C++ test since, given the large number and variety of existing C++ and Python tests, it is unlikely any of these missing tests will increase coverage. For example, there already exists two Python tests which involve the GDS import feature (test_bend_flux.py and test_prism.py). Also, gdsII-3d.cpp (one of the missing tests) has bit rotted and would need to be overhauled.

(Unfortunately, the Codecov service seems to be currently malfunctioning because the report for #1878 states that including ring-ll.cpp will reduce coverage by ~23% which is obviously incorrect.)

[stevengj]

I think these were added when meepgeom.cpp was created, before meepgeom was used by the Python API. Now that the Python API uses meepgeom.cpp, I think these tests are redundant?

I would be open to just deleting them, if someone goes through and double-checks that they are exercising functions that are also used by the Python API.