diff --git a/unittest/force-styles/CMakeLists.txt b/unittest/force-styles/CMakeLists.txt
index 66c4ddd2ce..294ece3a1f 100644
--- a/unittest/force-styles/CMakeLists.txt
+++ b/unittest/force-styles/CMakeLists.txt
@@ -79,6 +79,7 @@ else()
   set(FORCE_TEST_ENVIRONMENT PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH})
 endif()
 list(APPEND FORCE_TEST_ENVIRONMENT "PYTHONUNBUFFERED=1")
+list(APPEND FORCE_TEST_ENVIRONMENT "PYTHONDONTWRITEBYTECODE=1")
 list(APPEND FORCE_TEST_ENVIRONMENT "OMP_PROC_BIND=false")
 list(APPEND FORCE_TEST_ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR}")
 get_property(BUILD_IS_MULTI_CONFIG GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
@@ -213,7 +214,7 @@ foreach(TEST ${FIX_TIMESTEP_TESTS})
 if(WIN32)
   set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}\\\;${LAMMPS_PYTHON_DIR}")
 else()
-  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:${LAMMPS_PYTHON_DIR}:$ENV{PYTHONPATH}")
+  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:${LAMMPS_PYTHON_DIR}:$ENV{PYTHONPATH};PYTHONDONTWRITEBYTECODE=1")
 endif()
   set_tests_properties(${TNAME} PROPERTIES LABELS "${TEST_TAGS}")
 endforeach()
@@ -231,7 +232,7 @@ foreach(TEST ${DIHEDRAL_TESTS})
     continue()
   endif()
   add_test(NAME ${TNAME} COMMAND test_dihedral_style ${TEST})
-  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH}")
+  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH};PYTHONDONTWRITEBYTECODE=1")
   set_tests_properties(${TNAME} PROPERTIES LABELS "${TEST_TAGS}")
 endforeach()
 
@@ -248,7 +249,7 @@ foreach(TEST ${IMPROPER_TESTS})
     continue()
   endif()
   add_test(NAME ${TNAME} COMMAND test_improper_style ${TEST})
-  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH}")
+  set_tests_properties(${TNAME} PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR};PYTHONPATH=${TEST_INPUT_FOLDER}:$ENV{PYTHONPATH};PYTHONDONTWRITEBYTECODE=1")
   set_tests_properties(${TNAME} PROPERTIES LABELS "${TEST_TAGS}")
 endforeach()
 
@@ -256,6 +257,6 @@ if(MLIAP_ENABLE_PYTHON AND (NOT WIN32))
   add_executable(test_mliappy_unified test_mliappy_unified.cpp)
   target_link_libraries(test_mliappy_unified PRIVATE lammps GTest::GMockMain)
   add_test(NAME TestMliapPyUnified COMMAND test_mliappy_unified)
-  set_tests_properties(TestMliapPyUnified PROPERTIES ENVIRONMENT "PYTHONPATH=${LAMMPS_PYTHON_DIR}:${LAMMPS_LIB_DIR}/cython")
+  set_tests_properties(TestMliapPyUnified PROPERTIES ENVIRONMENT "PYTHONPATH=${LAMMPS_PYTHON_DIR};PYTHONDONTWRITEBYTECODE=1")
 endif()
 
diff --git a/unittest/python/CMakeLists.txt b/unittest/python/CMakeLists.txt
index 0aebc6fc7c..78b0d18446 100644
--- a/unittest/python/CMakeLists.txt
+++ b/unittest/python/CMakeLists.txt
@@ -44,6 +44,7 @@ else()
 endif()
 list(APPEND PYTHON_TEST_ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR}")
 list(APPEND PYTHON_TEST_ENVIRONMENT "PYTHONUNBUFFERED=1")
+list(APPEND PYTHON_TEST_ENVIRONMENT "PYTHONDONTWRITEBYTECODE=1")
 if(APPLE)
   list(APPEND PYTHON_TEST_ENVIRONMENT "DYLD_LIBRARY_PATH=${LAMMPS_LIB_PATH}:$ENV{DYLD_LIBRARY_PATH}")
 elseif(WIN32)