diff --git a/HISTORY.rst b/HISTORY.rst
index ef4e815d..2b307a33 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -26,7 +26,8 @@ PlatformIO Core 6
 
 * **Unit Testing**
 
-  - Merged the |UNITTESTING| "building" stage with "uploading" for the embedded target (`issue #4307 <https://github.com/platformio/platformio-core/issues/4307>`_)
+  - Export |UNITTESTING| flags only to the project build environment (``projenv``, files in "src" folder)
+  - Merged the "building" stage with "uploading" for the embedded target (`issue #4307 <https://github.com/platformio/platformio-core/issues/4307>`_)
   - Do not resolve dependencies from the project "src" folder when the `test_build_src <https://docs.platformio.org/en/latest//projectconf/section_env_test.html#test-build-src>`__ option is not enabled
   - Fixed an issue when a custom `pio test --project-config <https://docs.platformio.org/en/latest/core/userguide/cmd_test.html#cmdoption-pio-test-c>`__ was not handled properly (`issue #4299 <https://github.com/platformio/platformio-core/issues/4299>`_)
 
diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 7269c708..addc3ce8 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -867,6 +867,8 @@ class ProjectAsLibBuilder(LibBuilderBase):
         project_src_filter = env.get("SRC_FILTER")
         super().__init__(env, *args, **kwargs)
         self.env["SRC_FILTER"] = project_src_filter
+        if "test" in self.env.GetBuildType():
+            self.env.ConfigureTestTarget()
 
     @classmethod
     def get_instance(cls, *args, **kwargs):
diff --git a/platformio/builder/tools/platformio.py b/platformio/builder/tools/platformio.py
index e6c9d7ba..c08c7438 100644
--- a/platformio/builder/tools/platformio.py
+++ b/platformio/builder/tools/platformio.py
@@ -126,8 +126,6 @@ def ProcessProgramDeps(env):
 
     if "debug" in env.GetBuildType():
         env.ConfigureDebugTarget()
-    if "test" in env.GetBuildType():
-        env.ConfigureTestTarget()
 
     # remove specified flags
     env.ProcessUnFlags(env.get("BUILD_UNFLAGS"))