--- CMakeLists.txt.orig	2025-12-19 16:57:53 UTC
+++ CMakeLists.txt
@@ -56,6 +56,10 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" )
 
 	# Linux: nothing to do here
 
+elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "FreeBSD" OR ${CMAKE_SYSTEM_NAME} STREQUAL "NetBSD" )
+
+    # FreeBSD and NetBSD: nothing to do here
+
 elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "OpenBSD" )
 
 	set_property ( GLOBAL PROPERTY FIND_LIBRARY_USE_OPENBSD_VERSIONING 1 )
@@ -159,23 +163,37 @@ endif ()
 # ---- Setup Google Testing
 #
 
+include( CTest )
+
 # For Windows: Prevent overriding the parent project's compiler/linker settings
 set( gtest_force_shared_crt ON CACHE BOOL "" FORCE )
 
-# Check if population has already been performed
-FetchContent_GetProperties(googletest)
-if ( NOT googletest_POPULATED )
-	# Fetch the content using previously declared details
-	FetchContent_MakeAvailable(googletest)
+option( EINSTEIN_FETCH_GTEST "Download googletest if not found" ON )
 
-	# Bring the populated content into the build
-	#add_subdirectory( ${googletest_SOURCE_DIR} ${googletest_BINARY_DIR} )
-endif ()
+set( EINSTEIN_USE_GTEST OFF )
+if ( BUILD_TESTING )
+	# Try to find GTest installed on the system first.
+	find_package( GTest CONFIG QUIET )
 
-enable_testing()
+	# Check if population has already been performed
+	if ( NOT GTest_FOUND AND EINSTEIN_FETCH_GTEST )
+		FetchContent_GetProperties(googletest)
+		if ( NOT googletest_POPULATED )
+			# Fetch the content using previously declared details
+			FetchContent_MakeAvailable(googletest)
 
-include( GoogleTest )
+			# Bring the populated content into the build
+			#add_subdirectory( ${googletest_SOURCE_DIR} ${googletest_BINARY_DIR} )
+		endif ()
+	endif ()
 
+	if ( TARGET GTest::gtest_main OR TARGET gtest_main )
+		set( EINSTEIN_USE_GTEST ON )
+	else ()
+		message( STATUS "GoogleTest not available; tests disabled." )
+	endif ()
+endif ()
+
 #
 # ---- Newt/64 library ---------------------------------------------------------
 #
@@ -322,11 +340,13 @@ if ( ${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" )
 		${app_sources}
 		${cmake_sources}
 	)
-	add_executable ( EinsteinTests
-		${common_sources}
-		${test_sources}
-		${cmake_sources}
-	)
+	if ( EINSTEIN_USE_GTEST )
+		add_executable ( EinsteinTests
+			${common_sources}
+			${test_sources}
+			${cmake_sources}
+		)
+	endif ()
 	if ( EINSTEIN_FLTK_FRONTEND )
 		add_library ( EinsteinFLGUI STATIC
 			${fluid_sources}
@@ -337,9 +357,11 @@ if ( ${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" )
 	target_compile_options( Einstein PUBLIC
 		-Wall -Wextra -Wpedantic -Wno-missing-field-initializers -Werror
 	)
-	target_compile_options( EinsteinTests PUBLIC
-		-Wall -Wextra -Wpedantic -Wno-missing-field-initializers -Werror
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_options( EinsteinTests PUBLIC
+			-Wall -Wextra -Wpedantic -Wno-missing-field-initializers -Werror
+		)
+	endif ()
 	if ( EINSTEIN_FLTK_FRONTEND )
 		target_compile_options( EinsteinFLGUI PUBLIC
 			-Wall -Wextra -Wpedantic -Wno-missing-field-initializers -Werror
@@ -357,10 +379,12 @@ if ( ${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" )
 			TARGET_OS_MAC=1 NS_BLOCK_ASSERTIONS=1
 		)
 	endif ()
-	target_compile_definitions ( EinsteinTests PRIVATE
-		TARGET_UI_FLTK=1 NO_PORT_AUDIO NO_X11 TARGET_OS_OPENSTEP=1
-		TARGET_OS_MAC=1 NS_BLOCK_ASSERTIONS=1
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_definitions ( EinsteinTests PRIVATE
+			TARGET_UI_FLTK=1 NO_PORT_AUDIO NO_X11 TARGET_OS_OPENSTEP=1
+			TARGET_OS_MAC=1 NS_BLOCK_ASSERTIONS=1
+		)
+	endif ()
 	if ( EINSTEIN_FLTK_FRONTEND )
 		target_compile_definitions ( EinsteinFLGUI PRIVATE
 			TARGET_UI_FLTK=1 NO_PORT_AUDIO NO_X11 TARGET_OS_OPENSTEP=1
@@ -390,7 +414,7 @@ if ( ${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" )
 			$ENV{ANDROID_NDK_HOME}/sysroot/usr/include
 		)
 	endif ()
-	if ( EINSTEIN_FLTK_FRONTEND )
+	if ( EINSTEIN_USE_GTEST AND EINSTEIN_FLTK_FRONTEND )
 		target_link_libraries ( EinsteinTests
 			${system_libs}
 			fltk::fltk
@@ -423,7 +447,7 @@ if ( ${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" )
 		)
 	endif ()
 
-elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CMAKE_SYSTEM_NAME} STREQUAL "OpenBSD" )
+elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CMAKE_SYSTEM_NAME} MATCHES ".*BSD$" )
 
 	# create the application
 	add_executable ( Einstein
@@ -431,11 +455,13 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CM
 		${app_sources}
 		${cmake_sources}
 	)
-	add_executable ( EinsteinTests
-		${common_sources}
-		${test_sources}
-		${cmake_sources}
-	)
+	if ( EINSTEIN_USE_GTEST )
+		add_executable ( EinsteinTests
+			${common_sources}
+			${test_sources}
+			${cmake_sources}
+		)
+	endif ()
 	add_library ( EinsteinFLGUI STATIC
 		${fluid_sources}
 	)
@@ -443,23 +469,34 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CM
 	# how to compile and link
 	target_compile_options ( Einstein PUBLIC
 		-Wall -Wno-multichar -Wno-misleading-indentation -Wno-unused-result
-		-Wno-missing-field-initializers -Wno-stringop-truncation # -Werror
+		-Wno-missing-field-initializers # -Werror
 		# Werror is disabled for testing purposes. Must reenable as soon as all Linux warnings are fixed.
 	)
-	target_compile_options ( EinsteinTests PUBLIC
-		-Wall -Wno-multichar -Wno-misleading-indentation -Wno-unused-result
-		-Wno-missing-field-initializers -Wno-stringop-truncation -Werror
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_options ( EinsteinTests PUBLIC
+			-Wall -Wno-multichar -Wno-misleading-indentation -Wno-unused-result
+			-Wno-missing-field-initializers -Werror
+		)
+	endif ()
 	target_compile_options ( EinsteinFLGUI PUBLIC
 		-Wall -Wno-multichar -Wno-misleading-indentation -Wno-unused-result
-		-Wno-missing-field-initializers -Wno-stringop-truncation -Werror
+		-Wno-missing-field-initializers -Werror
 	)
+	if (CMAKE_C_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+        target_compile_options(Einstein PUBLIC -Wno-stringop-truncation)
+		if ( EINSTEIN_USE_GTEST )
+			target_compile_options(EinsteinTests PUBLIC -Wno-stringop-truncation)
+		endif ()
+        target_compile_options(EinsteinFLGUI PUBLIC -Wno-stringop-truncation)
+    endif()
 	target_compile_definitions ( Einstein PRIVATE
 		TARGET_UI_FLTK=1 TARGET_OS_LINUX=1
 	)
-	target_compile_definitions ( EinsteinTests PRIVATE
-		TARGET_UI_FLTK=1 TARGET_OS_LINUX=1
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_definitions ( EinsteinTests PRIVATE
+			TARGET_UI_FLTK=1 TARGET_OS_LINUX=1
+		)
+	endif ()
 	target_compile_definitions ( EinsteinFLGUI PRIVATE
 		TARGET_UI_FLTK=1 TARGET_OS_LINUX=1
 	)
@@ -469,18 +506,20 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CM
 		EinsteinFLGUI
 		pthread
 	)
-	target_link_libraries ( EinsteinTests
-		${system_libs}
-		fltk::fltk
-		EinsteinFLGUI
-		pthread
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_link_libraries ( EinsteinTests
+			${system_libs}
+			fltk::fltk
+			EinsteinFLGUI
+			pthread
+		)
+	endif ()
 	target_link_libraries ( EinsteinFLGUI
 		fltk::fltk fltk::images fltk::png fltk::z
 	)
 
-	if ( ${CMAKE_SYSTEM_NAME} STREQUAL "OpenBSD" )
-		# Under OpenBSD, libffi is in ports (i.e. /usr/local) not base (i.e. /usr)
+	if ( ${CMAKE_SYSTEM_NAME} MATCHES ".*BSD$" )
+		# Under BSD, libffi is in ports (i.e. /usr/local) not base (i.e. /usr)
 		find_library ( ffi_lib NAMES ffi )
 		find_file ( ffi_incl NAMES ffi.h )
 		if ( ffi_lib MATCHES ".*NOTFOUND" OR ffi_incl MATCHES ".*NOTFOUND" )
@@ -493,7 +532,7 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CM
 			target_link_libraries ( Einstein ${ffi_lib} )
 		endif ()
 
-		# Under OpenBSD, pulseaudio is in ports (i.e. /usr/local) not base (i.e. /usr)
+		# Under BSD, pulseaudio is in ports (i.e. /usr/local) not base (i.e. /usr)
 		find_library ( pulse_lib NAMES pulse )
 		if ( pulse_lib MATCHES ".*NOTFOUND" )
 			message ( FATAL_ERROR "libpulse not found! " )
@@ -503,7 +542,7 @@ elseif ( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" OR ${CM
 			target_link_libraries ( Einstein ${pulse_lib} )
 		endif ()
 
-		# Under OpenBSD, X11 is in /usr/X11R6
+		# Under BSD, find X11
 		include ( FindX11 )
 		if ( X11_FOUND )
 			target_include_directories ( Einstein SYSTEM PUBLIC ${X11_INCLUDE_DIR} )
@@ -527,30 +566,38 @@ elseif ( WIN32 )
 		${common_sources} ${app_sources} ${cmake_sources} ${data}
 		${CMAKE_CURRENT_BINARY_DIR}/Einstein.rc
 	)
-	add_executable ( EinsteinTests
-		${common_sources} ${test_sources}
-	)
+	if ( EINSTEIN_USE_GTEST )
+		add_executable ( EinsteinTests
+			${common_sources} ${test_sources}
+		)
+	endif ()
 	add_library ( EinsteinFLGUI STATIC
 		${fluid_sources}
 	)
 
 	# how to compile and link
 	target_compile_options( Einstein PUBLIC "/bigobj" )
-	target_compile_options( EinsteinTests PUBLIC "/bigobj" )
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_options( EinsteinTests PUBLIC "/bigobj" )
+	endif ()
 	target_compile_options( EinsteinFLGUI PUBLIC "/bigobj" )
 	if ( $<CONFIG:Debug> )
 		target_compile_options( Einstein PUBLIC "/ZI" )
-		target_compile_options( EinsteinTests PUBLIC "/ZI" )
+		if ( EINSTEIN_USE_GTEST )
+			target_compile_options( EinsteinTests PUBLIC "/ZI" )
+		endif ()
 		target_compile_options( EinsteinFLGUI PUBLIC "/ZI" )
 	endif ()
 	target_compile_definitions ( Einstein PRIVATE
 		TARGET_UI_FLTK=1 TARGET_OS_WIN32=1
 		WIN32_LEAN_AND_MEAN=1 _CRT_SECURE_NO_WARNINGS=1
 	)
-	target_compile_definitions ( EinsteinTests PRIVATE
-		TARGET_UI_FLTK=1 TARGET_OS_WIN32=1
-		WIN32_LEAN_AND_MEAN=1 _CRT_SECURE_NO_WARNINGS=1
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_compile_definitions ( EinsteinTests PRIVATE
+			TARGET_UI_FLTK=1 TARGET_OS_WIN32=1
+			WIN32_LEAN_AND_MEAN=1 _CRT_SECURE_NO_WARNINGS=1
+		)
+	endif ()
 	target_compile_definitions ( EinsteinFLGUI PRIVATE
 		TARGET_UI_FLTK=1 TARGET_OS_WIN32=1
 		WIN32_LEAN_AND_MEAN=1 _CRT_SECURE_NO_WARNINGS=1
@@ -562,17 +609,19 @@ elseif ( WIN32 )
 		winmm
 		gdiplus
 	)
-	target_link_libraries ( EinsteinTests
-		${system_libs}
-		fltk::fltk
-		EinsteinFLGUI
-		gdiplus
-	)
-	target_link_libraries ( EinsteinTests
-		${system_libs}
-		fltk::fltk
-		gdiplus
-	)
+	if ( EINSTEIN_USE_GTEST )
+		target_link_libraries ( EinsteinTests
+			${system_libs}
+			fltk::fltk
+			EinsteinFLGUI
+			gdiplus
+		)
+		target_link_libraries ( EinsteinTests
+			${system_libs}
+			fltk::fltk
+			gdiplus
+		)
+	endif ()
 	target_link_libraries ( EinsteinFLGUI
 		fltk::fltk fltk::images fltk::png fltk::z
 	)
@@ -634,11 +683,13 @@ target_include_directories (
 	${CMAKE_SOURCE_DIR}
 	${FLTK_INCLUDE_DIRS}
 )
-target_include_directories (
-	EinsteinTests PUBLIC
-	${CMAKE_SOURCE_DIR}
-	${FLTK_INCLUDE_DIRS}
-)
+if ( EINSTEIN_USE_GTEST )
+	target_include_directories (
+		EinsteinTests PUBLIC
+		${CMAKE_SOURCE_DIR}
+		${FLTK_INCLUDE_DIRS}
+	)
+endif ()
 if ( EINSTEIN_FLTK_FRONTEND )
 	target_include_directories (
 		EinsteinFLGUI PUBLIC
@@ -648,14 +699,27 @@ target_compile_definitions ( Einstein PUBLIC "$<$<CONF
 endif ()
 
 target_compile_definitions ( Einstein PUBLIC "$<$<CONFIG:DEBUG>:_DEBUG>" USE_CMAKE )
-target_compile_definitions ( EinsteinTests PUBLIC "$<$<CONFIG:DEBUG>:_DEBUG>" USE_CMAKE )
+if ( EINSTEIN_USE_GTEST )
+	target_compile_definitions ( EinsteinTests PUBLIC "$<$<CONFIG:DEBUG>:_DEBUG>" USE_CMAKE )
+endif ()
 if ( EINSTEIN_FLTK_FRONTEND )
 	target_compile_definitions ( EinsteinFLGUI PUBLIC "$<$<CONFIG:DEBUG>:_DEBUG>" USE_CMAKE )
 endif ()
 
-target_link_libraries ( EinsteinTests gtest_main )
+if ( EINSTEIN_USE_GTEST )
+	include( GoogleTest )
+	if ( TARGET GTest::gtest_main )
+		target_link_libraries ( EinsteinTests GTest::gtest_main )
+	elseif ( TARGET gtest_main )
+		target_link_libraries ( EinsteinTests gtest_main )
+	else ()
+		message ( STATUS "GoogleTest found without a gtest_main target; tests disabled." )
+	endif ()
+endif ()
 
-gtest_discover_tests ( EinsteinTests )
+if ( EINSTEIN_USE_GTEST AND ( TARGET GTest::gtest_main OR TARGET gtest_main ) )
+	gtest_discover_tests ( EinsteinTests )
+endif ()
 
 endif ()