Add LAMMPS_TESTING_SOURCE_DIR and LAMMPS_TESTING_GIT_TAG options

option(ENABLE_TESTING "Enable testing" OFF)

if(ENABLE_TESTING)

  enable_testing()

  option(LAMMPS_TESTING_SOURCE_DIR "Location of lammps-testing source directory" "")

  option(LAMMPS_TESTING_GIT_TAG    "Git tag of lammps-testing" "master")

  mark_as_advanced(LAMMPS_TESTING_SOURCE_DIR LAMMPS_TESTING_GIT_TAG)

  if (CMAKE_VERSION VERSION_GREATER "3.10.3") # due to FetchContent

  if (CMAKE_VERSION VERSION_GREATER "3.10.3" AND NOT LAMMPS_TESTING_SOURCE_DIR)

    include(FetchContent)

    FetchContent_Declare(lammps-testing

      GIT_REPOSITORY https://github.com/lammps/lammps-testing.git

      GIT_TAG master

      GIT_TAG ${LAMMPS_TESTING_GIT_TAG}

    )

    FetchContent_GetProperties(lammps-testing)

      message(STATUS "Downloading tests...")

      FetchContent_Populate(lammps-testing)

    endif()

    set(LAMMPS_TESTING_SOURCE_DIR ${lammps-testing_SOURCE_DIR})

  elseif(NOT LAMMPS_TESTING_SOURCE_DIR)

    message(WARNING "Full test-suite requires CMake >= 3.11 or copy of\n"

                    "https://github.com/lammps/lammps-testing in LAMMPS_TESTING_SOURCE_DIR")

  endif()

  if(EXISTS ${LAMMPS_TESTING_SOURCE_DIR})

    message(STATUS "Running test discovery...")

    file(GLOB_RECURSE TEST_SCRIPTS ${lammps-testing_SOURCE_DIR}/tests/core/*/in.*)

    file(GLOB_RECURSE TEST_SCRIPTS ${LAMMPS_TESTING_SOURCE_DIR}/tests/core/*/in.*)

    foreach(script_path ${TEST_SCRIPTS})

      get_filename_component(TEST_NAME ${script_path} EXT)

      get_filename_component(SCRIPT_NAME ${script_path} NAME)

      add_test(${TEST_NAME} ${CMAKE_BINARY_DIR}/${LAMMPS_BINARY} -in ${SCRIPT_NAME})

      set_tests_properties(${TEST_NAME} PROPERTIES WORKING_DIRECTORY ${PARENT_DIR})

    endforeach()

  else()

    message(WARNING "Full test-suite requires CMake >= 3.11")

    list(LENGTH TEST_SCRIPTS NUM_TESTS)

    message(STATUS "Found ${NUM_TESTS} tests.")

  endif()

endif(ENABLE_TESTING)