created an empty tester for improper style

unittest/force-styles/CMakeLists.txt

@@ -96,7 +96,7 @@ endforeach()
 add_executable(test_angle_style test_angle_style.cpp)
 target_link_libraries(test_angle_style PRIVATE lammps style_tests)
 
-file(GLOB ANGLE_TESTS LIST_DIRECTORIES false ${TEST_INPUT_FOLDER}/angle-*.yaml)
+file(GLOB IMPROPER_TESTS LIST_DIRECTORIES false ${TEST_INPUT_FOLDER}/angle-*.yaml)
 foreach(TEST ${ANGLE_TESTS})
   string(REGEX REPLACE "^.*angle-(.*)\.yaml" "AngleStyle:\\1" TNAME ${TEST})
   add_test(NAME ${TNAME} COMMAND test_angle_style ${TEST} WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
@@ -114,3 +114,14 @@ foreach(TEST ${KSPACE_TESTS})
   add_test(NAME ${TNAME} COMMAND test_pair_style ${TEST} WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
   set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH}")
 endforeach()
+
+# improper style tester
+add_executable(test_improper_style test_improper_style.cpp)
+target_link_libraries(test_improper_style PRIVATE lammps style_tests)
+
+file(GLOB IMPROPER_TESTS LIST_DIRECTORIES false ${TEST_INPUT_FOLDER}/improper-*.yaml)
+foreach(TEST ${IMPROPER_TESTS})
+  string(REGEX REPLACE "^.*improper-(.*)\.yaml" "ImproperStyle:\\1" TNAME ${TEST})
+  add_test(NAME ${TNAME} COMMAND test_improper_style ${TEST} WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH}")
+endforeach()

unittest/force-styles/test_improper_style.cpp

@@ -0,0 +1,108 @@
+/*
+- there are 7 basic functions
+  - delete_file
+  - cleanup_lammps
+  - init_lammps
+  - run_lammps
+  - restart_lammps
+  - data_lammps
+  - generate_yaml_file
+- move delete_file amd cleanup_lammps to a single file
+- I don't understand utility lambda, but they are being reused multiple times
+- add as many comments as possible, to show my understanding and document the code
+- code for matching forces, energy and stress are repeated 3 times
+- run_lammps looks to be same across all tests - it isn't, there's subtle difference
+*/
+
+/* ----------------------------------------------------------------------
+   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
+   http://lammps.sandia.gov, Sandia National Laboratories
+   Steve Plimpton, sjplimp@sandia.gov
+
+   Copyright (2003) Sandia Corporation.  Under the terms of Contract
+   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
+   certain rights in this software.  This software is distributed under
+   the GNU General Public License.
+
+   See the README file in the top-level LAMMPS directory.
+------------------------------------------------------------------------- */
+
+// unit tests for improper styles intended for molecular systems
+
+#include "error_stats.h"
+#include "test_config.h"
+#include "test_config_reader.h"
+#include "test_main.h"
+#include "yaml_reader.h"
+#include "yaml_writer.h"
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include "atom.h"
+#include "improper.h"
+#include "compute.h"
+#include "fmt/format.h"
+#include "force.h"
+#include "info.h"
+#include "input.h"
+#include "lammps.h"
+#include "modify.h"
+#include "universe.h"
+
+#include <cctype>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <mpi.h>
+
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
+using ::testing::HasSubstr;
+using ::testing::StartsWith;
+
+using namespace LAMMPS_NS;
+
+static void delete_file(const std::string &filename)
+{
+    remove(filename.c_str());
+};
+
+void cleanup_lammps(LAMMPS *lmp, const TestConfig &cfg)
+{
+    delete_file(cfg.basename + ".restart");
+    delete_file(cfg.basename + ".data");
+    delete_file(cfg.basename + "-coeffs.in");
+    delete lmp;
+}
+
+void run_lammps(LAMMPS *lmp)
+{
+    // 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 improper");
+    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");
+}
+
+LAMMPS *init_lammps(int argc, char **argv, const TestConfig &cfg, const bool newton = true){}
+
+void restart_lammps(LAMMPS *lmp, const TestConfig &cfg){}
+
+void data_lammps(LAMMPS *lmp, const TestConfig &cfg){}
+
+void generate_yaml_file(const char *outfile, const TestConfig &config){}
+
+TEST(ImproperStyle, plain){}
+TEST(ImproperStyle, omp){}
+TEST(ImproperStyle, single){}