diff --git a/CMakeModules/FlightGearComponent.cmake b/CMakeModules/FlightGearComponent.cmake
index cfb25ef66..dcb94bff8 100644
--- a/CMakeModules/FlightGearComponent.cmake
+++ b/CMakeModules/FlightGearComponent.cmake
@@ -23,6 +23,13 @@ macro(flightgear_component name sources)
         target_sources(fgfsObjects PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/${h})
     endforeach()
 
+    # third argument is TEST_SOURCES
+    foreach(t ${ARGV3})
+        set_property(GLOBAL
+            APPEND PROPERTY FG_TEST_SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/${t}")
+        set(fc "${fh}#${CMAKE_CURRENT_SOURCE_DIR}/${t}")
+    endforeach()
+
     set_property(GLOBAL APPEND PROPERTY FG_GROUPS_C "${fc}@")
     set_property(GLOBAL APPEND PROPERTY FG_GROUPS_H "${fh}@")
 
diff --git a/src/Airports/airport.cxx b/src/Airports/airport.cxx
index c6d3ec920..742039f39 100644
--- a/src/Airports/airport.cxx
+++ b/src/Airports/airport.cxx
@@ -989,17 +989,6 @@ void FGAirport::sortBySize(FGPositionedList& airportList)
     }
 }
 
-#if defined(BUILDING_TESTSUITE)
-
-void FGAirport::testSuiteInjectGroundnetXML(const SGPath& path)
-{
-    _groundNetwork.reset(new FGGroundNetwork(const_cast<FGAirport*>(this)));
-    XMLLoader::loadFromPath(_groundNetwork.get(), path);
-    _groundNetwork->init();
-}
-
-#endif
-
 FGAirportDynamicsRef FGAirport::getDynamics() const
 {
     return flightgear::AirportDynamicsManager::find(const_cast<FGAirport*>(this));
diff --git a/src/Airports/airport.hxx b/src/Airports/airport.hxx
index c36e8ad5e..a8c45fd93 100644
--- a/src/Airports/airport.hxx
+++ b/src/Airports/airport.hxx
@@ -317,11 +317,9 @@ class FGAirport : public FGPositioned
 
     static void clearAirportsCache();
 
-
-#if defined(BUILDING_TESTSUITE)
-    // helper to allow testing without needing a full Airports heirarchy
+    // helper to allow testing without needing a full Airports hierarchy
+    // only for use by the test-suite, not available outside of it.
     void testSuiteInjectGroundnetXML(const SGPath& path);
-#endif
 private:
     static flightgear::AirportCache airportCache;
 
diff --git a/src/Main/CMakeLists.txt b/src/Main/CMakeLists.txt
index 047da1e3f..308a19830 100644
--- a/src/Main/CMakeLists.txt
+++ b/src/Main/CMakeLists.txt
@@ -29,7 +29,6 @@ set(SOURCES
     subsystemFactory.cxx
     util.cxx
     XLIFFParser.cxx
-    sentryIntegration.cxx
     ErrorReporter.cxx
     ${MS_RESOURCE_FILE}
 )
@@ -51,13 +50,13 @@ set(HEADERS
     subsystemFactory.hxx
     util.hxx
     XLIFFParser.hxx
-    sentryIntegration.hxx
     ErrorReporter.hxx
+    sentryIntegration.hxx
 )
 
-flightgear_component(Main "${SOURCES}" "${HEADERS}")
+flightgear_component(Main "${SOURCES}" "${HEADERS}" sentryIntegration.cxx)
 
-# The main() function.
+# the main() function
 set(MAIN_SOURCE
     bootstrap.cxx
 )
@@ -68,12 +67,10 @@ setup_fgfs_embedded_resources()
 # Sort the sources and headers for MSVC.
 setup_msvc_grouping()
 
+# souerces which are different for fgfs vs the test-suite
+get_property(TEST_SOURCES GLOBAL PROPERTY FG_TEST_SOURCES)
 
 
-# # All sources and headers to be built into fgfs.
-# get_property(FG_SOURCES GLOBAL PROPERTY FG_SOURCES)
-# get_property(FG_HEADERS GLOBAL PROPERTY FG_HEADERS)
-
 # important we pass WIN32 here so the console is optional. Other
 # platforms ignore this option. If a console is needed we allocate
 # it manually via AllocConsole()
@@ -82,6 +79,7 @@ add_executable(fgfs
     WIN32
     MACOSX_BUNDLE
     ${MAIN_SOURCE}
+    ${TEST_SOURCES}
     $<TARGET_OBJECTS:fgfsObjects>
 )
 
diff --git a/src/Main/positioninit.hxx b/src/Main/positioninit.hxx
index 488592cba..7e7b0f20b 100644
--- a/src/Main/positioninit.hxx
+++ b/src/Main/positioninit.hxx
@@ -31,12 +31,9 @@ bool initPosition();
 // Listen to /sim/tower/airport-id and set tower view position accordingly
 void initTowerLocationListener();
 
-#if defined(BUILDING_TESTSUITE)
 // allow this to be manually invoked for position init testing
 void finalizePosition();
 
-#endif
-
 } // of namespace flightgear
 
 #endif // of FG_POSITION_INIT_HXX
diff --git a/src/Scripting/CMakeLists.txt b/src/Scripting/CMakeLists.txt
index 6a5bb2121..1c955acf0 100644
--- a/src/Scripting/CMakeLists.txt
+++ b/src/Scripting/CMakeLists.txt
@@ -1,7 +1,6 @@
 include(FlightGearComponent)
 
 set(SOURCES
-  NasalSys.cxx
   nasal-props.cxx
   NasalAddons.cxx
   NasalAircraft.cxx
@@ -47,5 +46,8 @@ else()
   endif()
 endif()
 
-flightgear_component(Scripting "${SOURCES}" "${HEADERS}")
+# NasalSys.cxx is passed as TEST_SOURCES since we need to compile it
+# seperately whrn building the test_suite
+
+flightgear_component(Scripting "${SOURCES}" "${HEADERS}"  NasalSys.cxx)
 
diff --git a/src/Scripting/NasalSys.hxx b/src/Scripting/NasalSys.hxx
index f59e1f33c..069c73bc9 100644
--- a/src/Scripting/NasalSys.hxx
+++ b/src/Scripting/NasalSys.hxx
@@ -153,11 +153,7 @@ public:
     simgear::BufferedLogCallback* log() const
     { return _log.get(); }
 
-#if defined(BUILDING_TESTSUITE)
-    /// test-suite only API: retrieve all Nasal runtime errors which
-    /// occurred since we last called this
     string_list getAndClearErrorList();
-#endif
 
 private:
     void initLogLevelConstants();
diff --git a/src/Time/TimeManager.hxx b/src/Time/TimeManager.hxx
index 9e749fe9f..766009fb1 100644
--- a/src/Time/TimeManager.hxx
+++ b/src/Time/TimeManager.hxx
@@ -58,9 +58,8 @@ public:
     double getSimSpeedUpFactor() const;
 private:
     // test class is a friend so we can fake elapsed system time
-#if defined(BUILDING_TESTSUITE)
     friend class TimeManagerTests;
-#endif
+
     /**
      * Ensure a consistent update-rate using a combination of
      * sleep()-ing and busy-waiting.  
diff --git a/test_suite/CMakeLists.txt b/test_suite/CMakeLists.txt
index 37783e483..3701b5fe5 100644
--- a/test_suite/CMakeLists.txt
+++ b/test_suite/CMakeLists.txt
@@ -111,18 +111,19 @@ setup_fgfs_embedded_resources()
 # Sort the sources and headers for MSVC.
 setup_msvc_grouping()
 
+# most object files come from fgfsObjects target: this property
+# contains all the sources which need to be compiled seperately
+# for the test-suite, becuase they depend on BUILDING_TESTSUTIE define
+# we setup below via target_compile_definitions
 
-
-# All sources and headers to be built into the test suite.
-get_property(FG_SOURCES GLOBAL PROPERTY FG_SOURCES)
-get_property(FG_HEADERS GLOBAL PROPERTY FG_HEADERS)
+get_property(TEST_SOURCES GLOBAL PROPERTY FG_TEST_SOURCES)
 
 # Set up the separate executable for running the test suite.
 add_executable(fgfs_test_suite
-    ${FG_SOURCES}
-    ${FG_HEADERS}
+    ${TEST_SOURCES}
     ${TESTSUITE_SOURCES}
     ${TESTSUITE_HEADERS}
+    $<TARGET_OBJECTS:fgfsObjects>
 )
 
 add_dependencies(fgfs_test_suite buildId)
diff --git a/test_suite/FGTestApi/CMakeLists.txt b/test_suite/FGTestApi/CMakeLists.txt
index 83074ce66..1205c0629 100644
--- a/test_suite/FGTestApi/CMakeLists.txt
+++ b/test_suite/FGTestApi/CMakeLists.txt
@@ -7,6 +7,7 @@ set(TESTSUITE_SOURCES
     ${CMAKE_CURRENT_SOURCE_DIR}/TestPilot.cxx
     ${CMAKE_CURRENT_SOURCE_DIR}/NasalUnitTesting_TestSuite.cxx
     ${CMAKE_CURRENT_SOURCE_DIR}/TestDataLogger.cxx
+    ${CMAKE_CURRENT_SOURCE_DIR}/testApis.cxx
     PARENT_SCOPE
 )
 
diff --git a/test_suite/FGTestApi/testApis.cxx b/test_suite/FGTestApi/testApis.cxx
new file mode 100644
index 000000000..44cec3e0e
--- /dev/null
+++ b/test_suite/FGTestApi/testApis.cxx
@@ -0,0 +1,16 @@
+
+#include "config.h"
+
+// implement various test-only methods on classes
+
+#include <Airports/groundnetwork.hxx>
+#include <Airports/airport.hxx>
+#include <Airports/xmlloader.hxx>
+
+void FGAirport::testSuiteInjectGroundnetXML(const SGPath& path)
+{
+    _groundNetwork.reset(new FGGroundNetwork(const_cast<FGAirport*>(this)));
+    XMLLoader::loadFromPath(_groundNetwork.get(), path);
+    _groundNetwork->init();
+}
+