Export a "PIO_UNIT_TESTING" macro to the project source files and dependent libraries in the Unit Testing mode

platformio/builder/tools/piolib.py

@@ -145,6 +145,10 @@ class LibBuilderBase:
         self._circular_deps = []
         self._processed_search_files = []
 
+        # pass a macro to the projenv + libs
+        if "test" in env.GetBuildType():
+            self.env.Append(CPPDEFINES=["PIO_UNIT_TESTING"])
+
         # reset source filter, could be overridden with extra script
         self.env["SRC_FILTER"] = ""
 

platformio/builder/tools/piotest.py

@@ -23,7 +23,7 @@ from platformio.test.runners.factory import TestRunnerFactory
 
 def ConfigureTestTarget(env):
     env.Append(
-        CPPDEFINES=["UNIT_TEST", "PIO_UNIT_TESTING"],
+        CPPDEFINES=["UNIT_TEST"],  # deprecated, use PIO_UNIT_TESTING
         PIOTEST_SRC_FILTER=[f"+<*.{ext}>" for ext in piotool.SRC_BUILD_EXT],
     )
     env.Prepend(CPPPATH=["$PROJECT_TEST_DIR"])