Unit tests depend on the global PARAM singleton

[Critsium-xy]

Describe the Code Quality Issue

A large number of unit tests directly reference and mutate the global singleton PARAM (extern Parameter PARAM, declared in source/source_io/module_parameter/parameter.h:50). Unit tests should not depend on global program state, but this pattern is pervasive across almost every module.

Parameter is deliberately designed to be read-only to the rest of the program:

class Parameter {
  public:
    // We can only read the value of input, but cannot modify it.
    const Input_para& inp = input;
    const MD_para&     mdp = input.mdp;
    const System_para& globalv = sys;
    ...
  private:
    // Only ReadInput and CalAtomInfo can modify the value of Parameter.
    // Do not add extra friend class here!!!
    friend class ModuleIO::ReadInput;
    friend class CalAtomsInfo;

    Input_para  input;   // private
    System_para sys;     // private
};
extern Parameter PARAM;

The data members input and sys are private, and only two friend classes are allowed to modify them — the header explicitly warns Do not add extra friend class here!!!.

Additional Context

Despite this, unit tests bypass the design in two compounding ways:

1. Global-state dependency. Tests read from and write to the global PARAM in their SetUp() in order to drive the code under test. This makes tests order-dependent, non-hermetic, and hard to parallelize, because one test's mutation of PARAM leaks into others through a process-wide singleton.

2. Encapsulation breakage via #define private public. Because input/sys are private, tests that need to set configuration (PARAM.input.xxx = ..., PARAM.sys.xxx = ...) resort to #define private public before including headers, defeating the access control the class was built to enforce.

Scale of the problem:

Metric	Count
Test files referencing PARAM	78 .cpp + 1 .h
Total PARAM references in tests	~1356
PARAM.input.* accesses (writes to private member)	1149
PARAM.sys.* accesses (writes to private member)	181
PARAM.globalv / PARAM.mdp (read-only interface)	31
Test files using #define private public	93

Affected files

source_estate (most affected)

File	Refs
source/source_estate/test/charge_mixing_test.cpp	325
source/source_estate/test/elecstate_base_test.cpp	67
source/source_estate/test/elecstate_print_test.cpp	40
source/source_estate/test/potential_new_test.cpp	25
source/source_estate/test/charge_extra_test.cpp	24
source/source_estate/test/elecstate_energy_test.cpp	20
source/source_estate/test/charge_test.cpp	19
source/source_estate/test/elecstate_pw_test.cpp	16
source/source_estate/test/elecstate_magnetism_test.cpp	12
source/source_estate/test_mpi/charge_mpi_test.cpp	7
source/source_estate/test/elecstate_occupy_test.cpp	3

source_cell

File	Refs
source/source_cell/test/unitcell_test.cpp	99
source/source_cell/test/unitcell_test_readpp.cpp	88
source/source_cell/test/klist_test.cpp	68
source/source_cell/test/unitcell_test_para.cpp	12
source/source_cell/module_neighbor/test/sltk_grid_test.cpp	7
source/source_cell/test/pseudo_nc_test.cpp	5
source/source_cell/test/read_pp_test.cpp	5
source/source_cell/test_pw/unitcell_test_pw.cpp	4
source/source_cell/test/unitcell_test_setupcell.cpp	4
source/source_cell/test/atom_pseudo_test.cpp	4
source/source_cell/test/klist_test_para.cpp	4
source/source_cell/module_neighbor/test/sltk_atom_arrange_test.cpp	3
source/source_cell/test/read_atoms_helper_test.cpp	1
source/source_cell/test/atom_spec_test.cpp	1

source_io

File	Refs
source/source_io/test/to_qo_test.cpp	148
source/source_io/test/print_info_test.cpp	28
source/source_io/test/read_wfc_pw_test.cpp	19
source/source_io/test/write_wfc_nao_test.cpp	14
source/source_io/test/write_dos_pw_test.cpp	14
source/source_io/test/write_hs_r_compat_test.cpp	12
source/source_io/module_json/test/para_json_test.cpp	8
source/source_io/test/read_wf2rho_pw_test.cpp	8
source/source_io/test/write_eig_occ_test.cpp	8
source/source_io/test/write_orb_info_test.cpp	7
source/source_io/test/read_wfc_nao_test.cpp	4
source/source_io/test_serial/read_input_test.cpp	3
source/source_io/test/outputlog_test.cpp	3
source/source_io/test/read_rhog_test.cpp	3
source/source_io/test/read_input_ptest.cpp	2
source/source_io/module_dm/test/write_dmk_test.cpp	2
source/source_io/test/single_R_io_test.cpp	1

source_hsolver

File	Refs
source/source_hsolver/test/test_hsolver_pw.cpp	14
source/source_hsolver/test/test_hsolver_sdft.cpp	5
source/source_hsolver/test/diago_pexsi_test.cpp	4
source/source_hsolver/test/diago_lcao_test.cpp	2
source/source_hsolver/test/diago_lcao_cusolver_test.cpp	2
source/source_hsolver/test/diago_lapack_test.cpp	2
source/source_hsolver/test/diago_cg_test.cpp	2
source/source_hsolver/test/diago_cg_real_test.cpp	2
source/source_hsolver/test/diago_cg_float_test.cpp	2

source_relax

File	Refs
source/source_relax/test/lattice_change_basic_test.cpp	15
source/source_relax/test/ions_move_bfgs_test.cpp	15
source/source_relax/test/ions_move_basic_test.cpp	9
source/source_relax/test/relax_test.cpp	5
source/source_relax/test/ions_move_sd_test.cpp	4
source/source_relax/test/bfgs_basic_test.cpp	3
source/source_relax/test/ions_move_cg_test.cpp	1
source/source_relax/test/bfgs_test.cpp	1

source_md

File	Refs
source/source_md/test/verlet_test.cpp	3
source/source_md/test/nhchain_test.cpp	3
source/source_md/test/msst_test.cpp	3
source/source_md/test/langevin_test.cpp	3
source/source_md/test/fire_test.cpp	3
source/source_md/test/md_func_test.cpp	2
source/source_md/test/setcell.h	5 (header)

source_lcao

File	Refs
source/source_lcao/module_deepks/test/deepks_test_prep.cpp	6
source/source_lcao/module_dftu/test/dftu_pw_test.cpp	3
source/source_lcao/module_operator_lcao/test/test_dftu.cpp	3
source/source_lcao/module_rt/test/propagator_test1.cpp	2
source/source_lcao/module_rt/test/propagator_test2.cpp	2
source/source_lcao/module_rt/test/propagator_test3.cpp	2
source/source_lcao/module_deepks/test/deepks_test_edelta.cpp	1

Other modules

File	Refs
source/source_psi/test/psi_initializer_unit_test.cpp	50
source/source_base/libm/test/libm_test.cpp	29
source/source_hamilt/module_surchem/test/cal_vel_test.cpp	2
source/source_basis/module_ao/test/ORB_atomic_lm_test.cpp	2
source/source_basis/module_ao/test/ORB_nonlocal_lm_test.cpp	1
source/source_pw/module_pwdft/test/structure_factor_test.cpp	1

Task list for Issue attackers (only for developers)

• Identify the specific code file or section with the code quality issue.
• Investigate the issue and determine the root cause.
• Research best practices and potential solutions for the identified issue.
• Refactor the code to improve code quality, following the suggested solution.
• Ensure the refactored code adheres to the project's coding standards.
• Test the refactored code to ensure it functions as expected.
• Update any relevant documentation, if necessary.
• Submit a pull request with the refactored code and a description of the changes made.