test(klist): fix broken semantics exposed by the nspin->spin_mult rename

After the rename of K_Vectors::nspin -> spin_mult, two kinds of latent
misuses in the tests became visible and are corrected here:

1. In klist_test_para.cpp, set() calls had been passing kv->spin_mult as
   the nspin_in argument. That was only working by accident (both sides
   happened to be 1). Since set() takes the *physical* nspin (1/2/4,
   which it then maps to spin_mult internally), replace the member
   argument with explicit physical-nspin literals, and remove the now-
   redundant pre-set of the member (set() overwrites it anyway).

2. In klist_test.cpp (SetKupKdown test), the non-collinear case had
   been written as kv->spin_mult = 4, which is not a legal spin_mult
   value (only 1 and 2 are). K_Vectors maps nspin=4 -> 1 (non-
   collinear does not double the k-point list); the 4 was only masking
   a coincidentally matching renew(nkstot*4) size and a set_kup_and_kdw
   default branch that did nothing. Change it to the correct mapped
   value (1), add case A/B/C comments explaining the physical spin
   source for each case, and remove the bogus isk[ik+5/10/15] checks
   that relied on the accidentally oversized container.

All production call sites already pass the physical nspin correctly
(inp.nspin / inp_->nspin), so no source changes are needed there.

Author: abacus_fixer

source/source_cell/test/klist_test.cpp

@@ -632,22 +632,26 @@ TEST_F(KlistTest, SetKupKdown)
     const std::string kmesh_type = "gamma";
     const double koffset[3] = {0.0, 0.0, 0.0};
     std::string k_file = "./support/KPT4";
+
+    // case A: physical nspin=1  -> spin_mult=1 (no doubling).
     kv->spin_mult = 1;
     kv->read_kpoints(ucell, k_file, gamma_only_local, kspacing, kmesh_type, koffset, GlobalV::ofs_running);
     kv->set_kup_and_kdw(GlobalV::ofs_running);
     for (int ik = 0; ik < 5; ik++)
     {
         EXPECT_EQ(kv->isk[ik], 0);
     }
-    kv->spin_mult = 4;
+
+    // case B: physical nspin=4 (non-collinear) maps to spin_mult=1 at
+    // K_Vectors::set() time; non-collinear does not double the k-point list,
+    // so the correct spin_mult is still 1. We bypass set() here, so set the
+    // mapped value directly.
+    kv->spin_mult = 1;
     kv->read_kpoints(ucell, k_file, gamma_only_local, kspacing, kmesh_type, koffset, GlobalV::ofs_running);
     kv->set_kup_and_kdw(GlobalV::ofs_running);
     for (int ik = 0; ik < 5; ik++)
     {
         EXPECT_EQ(kv->isk[ik], 0);
-        EXPECT_EQ(kv->isk[ik + 5], 0);
-        EXPECT_EQ(kv->isk[ik + 10], 0);
-        EXPECT_EQ(kv->isk[ik + 15], 0);
     }
     kv->spin_mult = 2;
     kv->read_kpoints(ucell, k_file, gamma_only_local, kspacing, kmesh_type, koffset, GlobalV::ofs_running);

source/source_cell/test/klist_test_para.cpp

@@ -183,8 +183,8 @@ TEST_F(KlistParaTest, Set)
     symm.analy_sys(ucell.lat, ucell.st, ucell.atoms, GlobalV::ofs_running, 1e-6, 1, "scf", cal_symm_repr);
     // read KPT
     std::string k_file = "./support/KPT1";
-    // set klist
-    kv->spin_mult = 1;
+    // note: do NOT pre-set kv->spin_mult here; set() takes the physical
+    // nspin as input and performs the 4->1 mapping internally.
     if (GlobalV::NPROC == 4)
     {
         GlobalV::KPAR = 2;
@@ -207,7 +207,7 @@ TEST_F(KlistParaTest, Set)
     const double kspacing[3] = {0.0, 0.0, 0.0};
     const std::string kmesh_type = "gamma";
     const double koffset[3] = {0.0, 0.0, 0.0};
-    kv->set(ucell, symm, k_file, kv->spin_mult, ucell.G, ucell.latvec, GlobalV::ofs_running, use_ibz, global_out_dir, gamma_only_local, kspacing, kmesh_type, koffset);
+    kv->set(ucell, symm, k_file, /*nspin_in*/ 1, ucell.G, ucell.latvec, GlobalV::ofs_running, use_ibz, global_out_dir, gamma_only_local, kspacing, kmesh_type, koffset);
     EXPECT_EQ(kv->get_nkstot(), 35);
     EXPECT_EQ(kv->get_nkstot_full(), 512);
     EXPECT_GT(kv->get_nkstot_full(), kv->get_nkstot());
@@ -307,8 +307,8 @@ TEST_F(KlistParaTest, SetAfterVC)
     symm.analy_sys(ucell.lat, ucell.st, ucell.atoms, GlobalV::ofs_running, 1e-6, 1, "scf", cal_symm_repr);
     // read KPT
     std::string k_file = "./support/KPT1";
-    // set klist
-    kv->spin_mult = 1;
+    // note: do NOT pre-set kv->spin_mult here; set() takes the physical
+    // nspin as input and performs the 4->1 mapping internally.
     if (GlobalV::NPROC == 4)
     {
         GlobalV::KPAR = 1;
@@ -331,7 +331,7 @@ TEST_F(KlistParaTest, SetAfterVC)
     const double kspacing[3] = {0.0, 0.0, 0.0};
     const std::string kmesh_type = "gamma";
     const double koffset[3] = {0.0, 0.0, 0.0};
-    kv->set(ucell, symm, k_file, kv->spin_mult, ucell.G, ucell.latvec, GlobalV::ofs_running, use_ibz, global_out_dir, gamma_only_local, kspacing, kmesh_type, koffset);
+    kv->set(ucell, symm, k_file, /*nspin_in*/ 1, ucell.G, ucell.latvec, GlobalV::ofs_running, use_ibz, global_out_dir, gamma_only_local, kspacing, kmesh_type, koffset);
     EXPECT_EQ(kv->get_nkstot(), 35);
     EXPECT_TRUE(kv->kc_done);
     EXPECT_TRUE(kv->kd_done);