test: fixed pytest warning

[j8xixo12]

#28 caused by way which treated raw string literal is different between python2 and python3 interpreter
more detail can check PEP-414
Therefore \( \)....\[, \] such like these string in Regex pattern will be treated as invalid escape sequence,
I figure out two way to fix this issue,

1. replace \( by \\(
2. add prefix r into Regex pattern explicitly marked with the raw Unicode
   and I choose 2

[yungyuc]

I think you chose the second approach. Have you tested with a brand new build/run?

[j8xixo12]

I think you chose the second approach. Have you tested with a brand new build/run?

i tested in my own repo, here is the log

platform linux -- Python 3.7.5, pytest-6.2.1, py-1.10.0, pluggy-0.13.1 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /home/runner/work/turgon/turgon/spacetime
collecting ... collected 61 items

tests/test_celm_selm.py::CelmTC::test_bounding_se PASSED
tests/test_celm_selm.py::CelmTC::test_calc_so PASSED
tests/test_celm_selm.py::CelmTC::test_coordinates PASSED
.
.
.
tests/test_solution.py::PythonCustomSolverTC::test_se PASSED
tests/test_solution.py::PythonCustomSolverTC::test_xctr PASSED
tests/test_solution.py::SolverProxyTC::test_march PASSED
tests/test_solution.py::SolverProxyTC::test_march_fine_interface PASSED

============================== 61 passed in 6.04s ==============================

[yungyuc]

It seems that you totally resolved the unwanted warnings. I'd like to merge now.