diff --git a/unittest/force-styles/angle_style.cpp b/unittest/force-styles/angle_style.cpp
index d5e2059b2b..f5299d5b0e 100644
--- a/unittest/force-styles/angle_style.cpp
+++ b/unittest/force-styles/angle_style.cpp
@@ -51,16 +51,15 @@ using ::testing::HasSubstr;
 
 using namespace LAMMPS_NS;
 
+static void delete_file(const std::string & filename) {
+    remove(filename.c_str());
+};
+
 void cleanup_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    std::string name;
-
-    name = cfg.basename + ".restart";
-    remove(name.c_str());
-    name = cfg.basename + ".data";
-    remove(name.c_str());
-    name = cfg.basename + "-coeffs.in";
-    remove(name.c_str());
+    delete_file(cfg.basename + ".restart");
+    delete_file(cfg.basename + ".data");
+    delete_file(cfg.basename + "-coeffs.in");
     delete lmp;
 }
 
@@ -75,7 +74,7 @@ LAMMPS *init_lammps(int argc, char **argv,
     // check if prerequisite styles are available
     Info *info = new Info(lmp);
     int nfail = 0;
-    for (auto prerequisite : cfg.prerequisites) {
+    for (auto& prerequisite : cfg.prerequisites) {
         std::string style = prerequisite.second;
 
         // this is a test for angle styles, so if the suffixed
@@ -92,106 +91,128 @@ LAMMPS *init_lammps(int argc, char **argv,
     if (nfail > 0) {
         delete info;
         cleanup_lammps(lmp,cfg);
-        return NULL;
+        return nullptr;
     }
 
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){ 
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
+
     if (newton) {
-        lmp->input->one("variable newton_bond index on");
+        command("variable newton_bond index on");
     } else {
-        lmp->input->one("variable newton_bond index off");
+        command("variable newton_bond index off");
     }
 
-    std::string set_input_dir = "variable input_dir index ";
-    set_input_dir += INPUT_FOLDER;
-    lmp->input->one(set_input_dir.c_str());
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("variable input_dir index " + INPUT_FOLDER);
+
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
+    }
 
     std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
-    lmp->input->file(input_file.c_str());
+    parse_input_script(input_file);
 
-    std::string cmd("angle_style ");
-    cmd += cfg.angle_style;
-    lmp->input->one(cmd.c_str());
-    for (auto angle_coeff : cfg.angle_coeff) {
-        cmd = "angle_coeff " + angle_coeff;
-        lmp->input->one(cmd.c_str());
+    command("angle_style " + cfg.angle_style);
+
+    for (auto& angle_coeff : cfg.angle_coeff) {
+        command("angle_coeff " + angle_coeff);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
-    cmd = "write_restart " + cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_data " + cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_coeff " + cfg.basename + "-coeffs.in";
-    lmp->input->one(cmd.c_str());
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
+    command("write_restart " + cfg.basename + ".restart");
+    command("write_data " + cfg.basename + ".data");
+    command("write_coeff " + cfg.basename + "-coeffs.in");
 
     return lmp;
 }
 
 void run_lammps(LAMMPS *lmp)
 {
-    lmp->input->one("fix 1 all nve");
-    lmp->input->one("compute pe all pe/atom");
-    lmp->input->one("compute sum all reduce sum c_pe");
-    lmp->input->one("thermo_style custom step temp pe press c_sum");
-    lmp->input->one("thermo 2");
-    lmp->input->one("run 4 post no");
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){ 
+        lmp->input->one(line.c_str());
+    };
+
+    command("fix 1 all nve");
+    command("compute pe all pe/atom");
+    command("compute sum all reduce sum c_pe");
+    command("thermo_style custom step temp pe press c_sum");
+    command("thermo 2");
+    command("run 4 post no");
 }
 
 void restart_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    std::string cmd("read_restart ");
-    cmd += cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){ 
+        lmp->input->one(line.c_str());
+    };
+
+    command("clear");
+    command("read_restart " + cfg.basename + ".restart");
 
     if (!lmp->force->angle) {
-        cmd = "angle_style " + cfg.angle_style;
-        lmp->input->one(cmd.c_str());
+        command("angle_style " + cfg.angle_style);
     }
+
     if ((cfg.angle_style.substr(0,6) == "hybrid")
         || !lmp->force->angle->writedata) {
-        for (auto angle_coeff : cfg.angle_coeff) {
-            cmd = "angle_coeff " + angle_coeff;
-            lmp->input->one(cmd.c_str());
+        for (auto& angle_coeff : cfg.angle_coeff) {
+            command("angle_coeff " + angle_coeff);
         }
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
 }
 
 void data_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    lmp->input->one("variable angle_style delete");
-    lmp->input->one("variable data_file  delete");
-    lmp->input->one("variable newton_bond delete");
-    lmp->input->one("variable newton_bond index on");
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){ 
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
 
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("clear");
+    command("variable angle_style delete");
+    command("variable data_file  delete");
+    command("variable newton_bond delete");
+    command("variable newton_bond index on");
 
-    std::string cmd("variable angle_style index '");
-    cmd += cfg.angle_style + "'";
-    lmp->input->one(cmd.c_str());
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
+    }
 
-    cmd = "variable data_file index ";
-    cmd += cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
+    command("variable angle_style index '" + cfg.angle_style + "'");
+    command("variable data_file index " + cfg.basename + ".data");
 
     std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
-    lmp->input->file(input_file.c_str());
+    parse_input_script(input_file);
 
-    for (auto angle_coeff : cfg.angle_coeff) {
-        cmd = "angle_coeff " + angle_coeff;
-        lmp->input->one(cmd.c_str());
+    for (auto& angle_coeff : cfg.angle_coeff) {
+        command("angle_coeff " + angle_coeff);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
 }
 
 
@@ -207,7 +228,7 @@ void generate_yaml_file(const char *outfile, const TestConfig &config)
     if (!lmp) {
         std::cerr << "One or more prerequisite styles are not available "
             "in this LAMMPS configuration:\n";
-        for (auto prerequisite : config.prerequisites) {
+        for (auto& prerequisite : config.prerequisites) {
             std::cerr << prerequisite.first << "_style "
                       << prerequisite.second << "\n";
         }
@@ -235,21 +256,21 @@ void generate_yaml_file(const char *outfile, const TestConfig &config)
 
     // prerequisites
     block.clear();
-    for (auto prerequisite :  config.prerequisites) {
+    for (auto& prerequisite :  config.prerequisites) {
         block += prerequisite.first + " " + prerequisite.second + "\n";
     }
     writer.emit_block("prerequisites", block);
 
     // pre_commands
     block.clear();
-    for (auto command :  config.pre_commands) {
+    for (auto& command :  config.pre_commands) {
         block += command + "\n";
     }
     writer.emit_block("pre_commands", block);
 
     // post_commands
     block.clear();
-    for (auto command : config.post_commands) {
+    for (auto& command : config.post_commands) {
         block += command + "\n";
     }
     writer.emit_block("post_commands", block);
@@ -262,7 +283,7 @@ void generate_yaml_file(const char *outfile, const TestConfig &config)
 
     // angle_coeff
     block.clear();
-    for (auto angle_coeff : config.angle_coeff) {
+    for (auto& angle_coeff : config.angle_coeff) {
         block += angle_coeff + "\n";
     }
     writer.emit_block("angle_coeff", block);
@@ -270,7 +291,7 @@ void generate_yaml_file(const char *outfile, const TestConfig &config)
     // extract
     block.clear();
     std::stringstream outstr;
-    for (auto data : config.extract) {
+    for (auto& data : config.extract) {
         outstr << data.first << " " << data.second << std::endl;
     }
     writer.emit_block("extract", outstr.str());
@@ -336,7 +357,7 @@ TEST(AngleStyle, plain) {
     if (!lmp) {
         std::cerr << "One or more prerequisite styles are not available "
             "in this LAMMPS configuration:\n";
-        for (auto prerequisite : test_config.prerequisites) {
+        for (auto& prerequisite : test_config.prerequisites) {
             std::cerr << prerequisite.first << "_style "
                       << prerequisite.second << "\n";
         }
@@ -570,7 +591,7 @@ TEST(AngleStyle, omp) {
     if (!lmp) {
         std::cerr << "One or more prerequisite styles with /omp suffix\n"
             "are not available in this LAMMPS configuration:\n";
-        for (auto prerequisite : test_config.prerequisites) {
+        for (auto& prerequisite : test_config.prerequisites) {
             std::cerr << prerequisite.first << "_style "
                       << prerequisite.second << "\n";
         }
diff --git a/unittest/force-styles/bond_style.cpp b/unittest/force-styles/bond_style.cpp
index 07e3e28e1b..d44eec995d 100644
--- a/unittest/force-styles/bond_style.cpp
+++ b/unittest/force-styles/bond_style.cpp
@@ -51,16 +51,15 @@ using ::testing::HasSubstr;
 
 using namespace LAMMPS_NS;
 
+static void delete_file(const std::string & filename) {
+    remove(filename.c_str());
+};
+
 void cleanup_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    std::string name;
-
-    name = cfg.basename + ".restart";
-    remove(name.c_str());
-    name = cfg.basename + ".data";
-    remove(name.c_str());
-    name = cfg.basename + "-coeffs.in";
-    remove(name.c_str());
+    delete_file(cfg.basename + ".restart");
+    delete_file(cfg.basename + ".data");
+    delete_file(cfg.basename + "-coeffs.in");
     delete lmp;
 }
 
@@ -95,104 +94,125 @@ LAMMPS *init_lammps(int argc, char **argv,
         return nullptr;
     }
 
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
+
     if (newton) {
-        lmp->input->one("variable newton_bond index on");
+        command("variable newton_bond index on");
     } else {
-        lmp->input->one("variable newton_bond index off");
+        command("variable newton_bond index off");
     }
 
-    std::string set_input_dir = "variable input_dir index ";
-    set_input_dir += INPUT_FOLDER;
-    lmp->input->one(set_input_dir.c_str());
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("variable input_dir index " + INPUT_FOLDER);
 
-    std::string input_file = INPUT_FOLDER + "/" + cfg.input_file;
-
-    lmp->input->file(input_file.c_str());
-
-    std::string cmd("bond_style ");
-    cmd += cfg.bond_style;
-    lmp->input->one(cmd.c_str());
-    for (auto bond_coeff : cfg.bond_coeff) {
-        cmd = "bond_coeff " + bond_coeff;
-        lmp->input->one(cmd.c_str());
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
-    cmd = "write_restart " + cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_data " + cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_coeff " + cfg.basename + "-coeffs.in";
-    lmp->input->one(cmd.c_str());
+
+    std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
+    parse_input_script(input_file);
+
+    command("bond_style " + cfg.bond_style);
+
+    for (auto& bond_coeff : cfg.bond_coeff) {
+        command("bond_coeff " + bond_coeff);
+    }
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
+    command("write_restart " + cfg.basename + ".restart");
+    command("write_data " + cfg.basename + ".data");
+    command("write_coeff " + cfg.basename + "-coeffs.in");
 
     return lmp;
 }
 
 void run_lammps(LAMMPS *lmp)
 {
-    lmp->input->one("fix 1 all nve");
-    lmp->input->one("compute pe all pe/atom");
-    lmp->input->one("compute sum all reduce sum c_pe");
-    lmp->input->one("thermo_style custom step temp pe press c_sum");
-    lmp->input->one("thermo 2");
-    lmp->input->one("run 4 post no");
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
+    command("fix 1 all nve");
+    command("compute pe all pe/atom");
+    command("compute sum all reduce sum c_pe");
+    command("thermo_style custom step temp pe press c_sum");
+    command("thermo 2");
+    command("run 4 post no");
 }
 
 void restart_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    std::string cmd("read_restart ");
-    cmd += cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
+    command("clear");
+    command("read_restart " + cfg.basename + ".restart");
 
     if (!lmp->force->bond) {
-        cmd = "bond_style " + cfg.bond_style;
-        lmp->input->one(cmd.c_str());
+        command("bond_style " + cfg.bond_style);
     }
+
     if ((cfg.bond_style.substr(0,6) == "hybrid")
         || !lmp->force->bond->writedata) {
-        for (auto bond_coeff : cfg.bond_coeff) {
-            cmd = "bond_coeff " + bond_coeff;
-            lmp->input->one(cmd.c_str());
+        for (auto& bond_coeff : cfg.bond_coeff) {
+            command("bond_coeff " + bond_coeff);
         }
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
 }
 
 void data_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    lmp->input->one("variable bond_style delete");
-    lmp->input->one("variable data_file  delete");
-    lmp->input->one("variable newton_bond delete");
-    lmp->input->one("variable newton_bond index on");
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
 
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("clear");
+    command("variable bond_style delete");
+    command("variable data_file  delete");
+    command("variable newton_bond delete");
+    command("variable newton_bond index on");
 
-    std::string cmd("variable bond_style index '");
-    cmd += cfg.bond_style + "'";
-    lmp->input->one(cmd.c_str());
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
+    }
 
-    cmd = "variable data_file index ";
-    cmd += cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
+    command("variable bond_style index '" + cfg.bond_style + "'");
+    command("variable data_file index " + cfg.basename + ".data");
 
     std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
-    lmp->input->file(input_file.c_str());
+    parse_input_script(input_file);
 
-    for (auto bond_coeff : cfg.bond_coeff) {
-        cmd = "bond_coeff " + bond_coeff;
-        lmp->input->one(cmd.c_str());
+    for (auto& bond_coeff : cfg.bond_coeff) {
+        command("bond_coeff " + bond_coeff);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
 }
 
 // re-generate yaml file with current settings.
@@ -761,63 +781,68 @@ TEST(BondStyle, single) {
         GTEST_SKIP();
     }
 
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
     Bond *bond = lmp->force->bond;
 
     // now start over
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("clear");
-    lmp->input->one("variable newton_bond delete");
-    lmp->input->one("variable newton_bond index on");
+    command("clear");
+    command("variable newton_bond delete");
+    command("variable newton_bond index on");
 
-    std::string set_input_dir = "variable input_dir index ";
-    set_input_dir += INPUT_FOLDER;
-    lmp->input->one(set_input_dir.c_str());
-    for (auto pre_command : test_config.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("variable input_dir index " + INPUT_FOLDER);
 
-    lmp->input->one("atom_style molecular");
-    lmp->input->one("units ${units}");
-    lmp->input->one("boundary p p p");
-    lmp->input->one("newton ${newton_pair} ${newton_bond}");
-    lmp->input->one("special_bonds lj/coul "
-                    "${bond_factor} ${angle_factor} ${dihedral_factor}");
+    for (auto& pre_command : test_config.pre_commands) {
+        command(pre_command);
+    }
+
+    command("atom_style molecular");
+    command("units ${units}");
+    command("boundary p p p");
+    command("newton ${newton_pair} ${newton_bond}");
+    command("special_bonds lj/coul "
+            "${bond_factor} ${angle_factor} ${dihedral_factor}");
+
+    command("atom_modify map array");
+    command("region box block -10.0 10.0 -10.0 10.0 -10.0 10.0 units box");
 
-    lmp->input->one("atom_modify map array");
-    lmp->input->one("region box block -10.0 10.0 -10.0 10.0 -10.0 10.0 units box");
     char buf[10];
-    snprintf(buf,10,"%d",ntypes);
     std::string cmd("create_box 1 box");
     cmd += " bond/types ";
     snprintf(buf,10,"%d",nbondtypes);
     cmd += buf;
     cmd += " extra/bond/per/atom 2";
     cmd += " extra/special/per/atom 2";
-    lmp->input->one(cmd.c_str());
+    command(cmd);
 
-    lmp->input->one("pair_style zero 8.0");
-    lmp->input->one("pair_coeff * *");
+    command("pair_style zero 8.0");
+    command("pair_coeff * *");
 
-    cmd = "bond_style ";
-    cmd += test_config.bond_style;
-    lmp->input->one(cmd.c_str());
+    command("bond_style " + test_config.bond_style);
     bond = lmp->force->bond;
 
     for (auto bond_coeff : test_config.bond_coeff) {
-        cmd = "bond_coeff " + bond_coeff;
-        lmp->input->one(cmd.c_str());
+        command("bond_coeff " + bond_coeff);
     }
 
     // create (only) four atoms and two bonds
-    lmp->input->one("mass * 1.0");
-    lmp->input->one("create_atoms 1 single  5.0 -0.75  0.4 units box");
-    lmp->input->one("create_atoms 1 single  5.5  0.25 -0.1 units box");
-    lmp->input->one("create_atoms 1 single -5.0  0.75  0.4 units box");
-    lmp->input->one("create_atoms 1 single -5.5 -0.25 -0.1 units box");
-    lmp->input->one("create_bonds single/bond 1 1 2");
-    lmp->input->one("create_bonds single/bond 2 3 4");
-    for (auto post_command : test_config.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+    command("mass * 1.0");
+    command("create_atoms 1 single  5.0 -0.75  0.4 units box");
+    command("create_atoms 1 single  5.5  0.25 -0.1 units box");
+    command("create_atoms 1 single -5.0  0.75  0.4 units box");
+    command("create_atoms 1 single -5.5 -0.25 -0.1 units box");
+    command("create_bonds single/bond 1 1 2");
+    command("create_bonds single/bond 2 3 4");
+
+    for (auto& post_command : test_config.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     int idx1 = lmp->atom->map(1);
@@ -857,8 +882,8 @@ TEST(BondStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx4][2], fsingle*delz2, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 0.5 0.5 0.5 23456");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 0.5 0.5 0.5 23456");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
@@ -895,8 +920,8 @@ TEST(BondStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx4][2], fsingle*delz2, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 0.5 0.5 0.5 456963");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 0.5 0.5 0.5 456963");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
@@ -933,8 +958,8 @@ TEST(BondStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx4][2], fsingle*delz2, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 0.5 0.5 0.5 9726532");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 0.5 0.5 0.5 9726532");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
diff --git a/unittest/force-styles/pair_style.cpp b/unittest/force-styles/pair_style.cpp
index e1aa42879b..50e1c010c8 100644
--- a/unittest/force-styles/pair_style.cpp
+++ b/unittest/force-styles/pair_style.cpp
@@ -51,16 +51,15 @@ using ::testing::HasSubstr;
 
 using namespace LAMMPS_NS;
 
+static void delete_file(const std::string & filename) {
+    remove(filename.c_str());
+};
+
 void cleanup_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    std::string name;
-
-    name = cfg.basename + ".restart";
-    remove(name.c_str());
-    name = cfg.basename + ".data";
-    remove(name.c_str());
-    name = cfg.basename + "-coeffs.in";
-    remove(name.c_str());
+    delete_file(cfg.basename + ".restart");
+    delete_file(cfg.basename + ".data");
+    delete_file(cfg.basename + "-coeffs.in");
     delete lmp;
 }
 
@@ -75,7 +74,7 @@ LAMMPS *init_lammps(int argc, char **argv,
     // check if prerequisite styles are available
     Info *info = new Info(lmp);
     int nfail = 0;
-    for (auto prerequisite : cfg.prerequisites) {
+    for (auto& prerequisite : cfg.prerequisites) {
         std::string style = prerequisite.second;
 
         // this is a test for pair styles, so if the suffixed
@@ -95,103 +94,122 @@ LAMMPS *init_lammps(int argc, char **argv,
         return nullptr;
     }
 
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
+
     if (newton) {
-        lmp->input->one("variable newton_pair index on");
+        command("variable newton_pair index on");
     } else {
-        lmp->input->one("variable newton_pair index off");
+        command("variable newton_pair index off");
     }
 
-    std::string set_input_dir = "variable input_dir index ";
-    set_input_dir += INPUT_FOLDER;
-    lmp->input->one(set_input_dir.c_str());
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("variable input_dir index " + INPUT_FOLDER);
+
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
+    }
 
     std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
-    lmp->input->file(input_file.c_str());
+    parse_input_script(input_file);
 
-    std::string cmd("pair_style ");
-    cmd += cfg.pair_style;
-    lmp->input->one(cmd.c_str());
-    for (auto pair_coeff : cfg.pair_coeff) {
-        cmd = "pair_coeff " + pair_coeff;
-        lmp->input->one(cmd.c_str());
+    command("pair_style " + cfg.pair_style);
+
+    for (auto& pair_coeff : cfg.pair_coeff) {
+        command("pair_coeff " + pair_coeff);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
-    cmd = "write_restart " + cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_data " + cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
-    cmd = "write_coeff " + cfg.basename + "-coeffs.in";
-    lmp->input->one(cmd.c_str());
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
+    command("write_restart " + cfg.basename + ".restart");
+    command("write_data " + cfg.basename + ".data");
+    command("write_coeff " + cfg.basename + "-coeffs.in");
 
     return lmp;
 }
 
 void run_lammps(LAMMPS *lmp)
 {
-    lmp->input->one("fix 1 all nve");
-    lmp->input->one("compute pe all pe/atom");
-    lmp->input->one("compute sum all reduce sum c_pe");
-    lmp->input->one("thermo_style custom step temp pe press c_sum");
-    lmp->input->one("thermo 2");
-    lmp->input->one("run 4 post no");
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
+    command("fix 1 all nve");
+    command("compute pe all pe/atom");
+    command("compute sum all reduce sum c_pe");
+    command("thermo_style custom step temp pe press c_sum");
+    command("thermo 2");
+    command("run 4 post no");
 }
 
 void restart_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    std::string cmd("read_restart ");
-    cmd += cfg.basename + ".restart";
-    lmp->input->one(cmd.c_str());
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
+    command("clear");
+    command("read_restart " + cfg.basename + ".restart");
 
     if (!lmp->force->pair) {
-        cmd = "pair_style " + cfg.pair_style;
-        lmp->input->one(cmd.c_str());
+        command("pair_style " + cfg.pair_style);
     }
     if (!lmp->force->pair->restartinfo
         || !lmp->force->pair->writedata) {
-        for (auto pair_coeff : cfg.pair_coeff) {
-            cmd = "pair_coeff " + pair_coeff;
-            lmp->input->one(cmd.c_str());
+        for (auto& pair_coeff : cfg.pair_coeff) {
+            command("pair_coeff " + pair_coeff);
         }
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
 }
 
 void data_lammps(LAMMPS *lmp, const TestConfig &cfg)
 {
-    lmp->input->one("clear");
-    lmp->input->one("variable pair_style  delete");
-    lmp->input->one("variable data_file   delete");
-    lmp->input->one("variable newton_pair delete");
-    lmp->input->one("variable newton_pair index on");
+    // utility lambdas to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+    auto parse_input_script = [&](const std::string & filename){
+        lmp->input->file(filename.c_str());
+    };
 
-    for (auto pre_command : cfg.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    command("clear");
+    command("variable pair_style  delete");
+    command("variable data_file   delete");
+    command("variable newton_pair delete");
+    command("variable newton_pair index on");
 
-    std::string cmd("variable pair_style index '");
-    cmd += cfg.pair_style + "'";
-    lmp->input->one(cmd.c_str());
+    for (auto& pre_command : cfg.pre_commands) {
+        command(pre_command);
+    }
 
-    cmd = "variable data_file index ";
-    cmd += cfg.basename + ".data";
-    lmp->input->one(cmd.c_str());
+    command("variable pair_style index '" + cfg.pair_style + "'");
+    command("variable data_file index " + cfg.basename + ".data");
 
     std::string input_file = INPUT_FOLDER + PATH_SEP + cfg.input_file;
-    lmp->input->file(input_file.c_str());
+    parse_input_script(input_file);
 
-    for (auto pair_coeff : cfg.pair_coeff) {
-        cmd = "pair_coeff " + pair_coeff;
-        lmp->input->one(cmd.c_str());
+    for (auto& pair_coeff : cfg.pair_coeff) {
+        command("pair_coeff " + pair_coeff);
     }
-    for (auto post_command : cfg.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+    for (auto& post_command : cfg.post_commands) {
+        command(post_command);
+    }
+    command("run 0 post no");
 }
 
 // re-generate yaml file with current settings.
@@ -1011,62 +1029,73 @@ TEST(PairStyle, single) {
 
     // now start over
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("clear");
-    lmp->input->one("variable newton_pair delete");
-    lmp->input->one("variable newton_pair index on");
 
-    std::string set_input_dir = "variable input_dir index ";
-    set_input_dir += INPUT_FOLDER;
-    lmp->input->one(set_input_dir.c_str());
-    for (auto pre_command : test_config.pre_commands)
-        lmp->input->one(pre_command.c_str());
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
 
-    lmp->input->one("atom_style full");
-    lmp->input->one("units ${units}");
-    lmp->input->one("boundary p p p");
-    lmp->input->one("newton ${newton_pair} ${newton_bond}");
-    if (molecular) {
-        lmp->input->one("special_bonds lj/coul "
-                        "${bond_factor} ${angle_factor} ${dihedral_factor}");
+    command("clear");
+    command("variable newton_pair delete");
+    command("variable newton_pair index on");
+
+    command("variable input_dir index " + INPUT_FOLDER);
+
+    for (auto& pre_command : test_config.pre_commands) {
+        command(pre_command);
     }
-    lmp->input->one("atom_modify map array");
-    lmp->input->one("region box block -10.0 10.0 -10.0 10.0 -10.0 10.0 units box");
+
+    command("atom_style full");
+    command("units ${units}");
+    command("boundary p p p");
+    command("newton ${newton_pair} ${newton_bond}");
+
+    if (molecular) {
+        command("special_bonds lj/coul "
+                "${bond_factor} ${angle_factor} ${dihedral_factor}");
+    }
+
+    command("atom_modify map array");
+    command("region box block -10.0 10.0 -10.0 10.0 -10.0 10.0 units box");
+
     char buf[10];
     snprintf(buf,10,"%d",ntypes);
     std::string cmd("create_box ");
     cmd += buf;
     cmd += " box";
     if (molecular) {
-        cmd += " bond/types 1";
-        cmd += " extra/bond/per/atom 1";
-        cmd += " extra/special/per/atom 1";
+        cmd += " bond/types 1"
+               " extra/bond/per/atom 1"
+               " extra/special/per/atom 1";
     }
-    lmp->input->one(cmd.c_str());
+    command(cmd);
+
+    command("pair_style " + test_config.pair_style);
 
-    cmd = "pair_style ";
-    cmd += test_config.pair_style;
-    lmp->input->one(cmd.c_str());
     pair = lmp->force->pair;
 
-    for (auto pair_coeff : test_config.pair_coeff) {
-        cmd = "pair_coeff " + pair_coeff;
-        lmp->input->one(cmd.c_str());
+    for (auto& pair_coeff : test_config.pair_coeff) {
+        command("pair_coeff " + pair_coeff);
     }
 
     // create (only) two atoms
-    lmp->input->one("mass * 1.0");
-    lmp->input->one("create_atoms 1 single 0.0 -0.75  0.4 units box");
-    lmp->input->one("create_atoms 2 single 0.5  0.25 -0.1 units box");
-    lmp->input->one("set atom 1 charge -0.5");
-    lmp->input->one("set atom 2 charge  0.5");
+    command("mass * 1.0");
+    command("create_atoms 1 single 0.0 -0.75  0.4 units box");
+    command("create_atoms 2 single 0.5  0.25 -0.1 units box");
+    command("set atom 1 charge -0.5");
+    command("set atom 2 charge  0.5");
+
     if (molecular) {
-        lmp->input->one("create_bonds single/bond 1 1 2");
-        lmp->input->one("bond_style zero");
-        lmp->input->one("bond_coeff 1 2.0");
+        command("create_bonds single/bond 1 1 2");
+        command("bond_style zero");
+        command("bond_coeff 1 2.0");
     }
-    for (auto post_command : test_config.post_commands)
-        lmp->input->one(post_command.c_str());
-    lmp->input->one("run 0 post no");
+
+    for (auto& post_command : test_config.post_commands) {
+        command(post_command);
+    }
+
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     int idx1 = lmp->atom->map(1);
@@ -1094,8 +1123,8 @@ TEST(PairStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx2][2], fsingle*delz, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 1.0 1.0 1.0 723456");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 1.0 1.0 1.0 723456");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
@@ -1118,8 +1147,8 @@ TEST(PairStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx2][2], fsingle*delz, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 1.0 1.0 1.0 3456963");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 1.0 1.0 1.0 3456963");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
@@ -1142,8 +1171,8 @@ TEST(PairStyle, single) {
     EXPECT_FP_LE_WITH_EPS(f[idx2][2], fsingle*delz, epsilon);
 
     if (!verbose) ::testing::internal::CaptureStdout();
-    lmp->input->one("displace_atoms all random 0.5 0.5 0.5 9726532");
-    lmp->input->one("run 0 post no");
+    command("displace_atoms all random 0.5 0.5 0.5 9726532");
+    command("run 0 post no");
     if (!verbose) ::testing::internal::GetCapturedStdout();
 
     f = lmp->atom->f;
@@ -1201,8 +1230,8 @@ TEST(PairStyle, extract) {
     Pair *pair = lmp->force->pair;
     void *ptr = nullptr;
     int dim = 0;
-    for (auto extract : test_config.extract) {
-        ptr = pair->extract(extract.first.c_str(),dim);
+    for (auto& extract : test_config.extract) {
+        ptr = pair->extract(extract.first.c_str(), dim);
         EXPECT_NE(ptr, nullptr);
         EXPECT_EQ(dim, extract.second);
     }
@@ -1218,16 +1247,21 @@ TEST(PairStyle, extract) {
             pair->cutsq[i][j] = -1.0;
         }
     }
-    std::string cmd = "pair_style ";
-    cmd += test_config.pair_style;
-    lmp->input->one(cmd.c_str());
-    EXPECT_EQ(pair,lmp->force->pair);
 
-    for (auto pair_coeff : test_config.pair_coeff) {
-        cmd = "pair_coeff " + pair_coeff;
-        lmp->input->one(cmd.c_str());
+    // utility lambda to improve readability
+    auto command = [&](const std::string & line){
+        lmp->input->one(line.c_str());
+    };
+
+    command("pair_style " + test_config.pair_style);
+    EXPECT_EQ(pair, lmp->force->pair);
+
+    for (auto& pair_coeff : test_config.pair_coeff) {
+        command("pair_coeff " + pair_coeff);
     }
+
     pair->init();
+
     for (int i=1; i <= ntypes; ++i) {
         for (int j=1; j <= ntypes; ++j) {
             EXPECT_GE(pair->cutsq[i][j],0.0);