Fixed an issue when unknown transport is used for PIO Unit Testing // Resolve #3422

HISTORY.rst

@@ -26,6 +26,7 @@ PlatformIO Core 4
 * Fixed an issue when Python 2 does not keep encoding when converting ".ino" (`issue #3393 <https://github.com/platformio/platformio-core/issues/3393>`_)
 * Fixed an issue when ``"libArchive": false`` in "library.json" does not work (`issue #3403 <https://github.com/platformio/platformio-core/issues/3403>`_)
 * Fixed an issue when not all commands in `compilation database "compile_commands.json" <https://docs.platformio.org/page/integration/compile_commands.html>`__ use absolute paths (`pull #3415 <https://github.com/platformio/platformio-core/pull/3415>`_)
+* Fixed an issue when unknown transport is used for `PIO Unit Testing <https://docs.platformio.org/page/plus/unit-testing.html>`__ engine (`issue #3422 <https://github.com/platformio/platformio-core/issues/3422>`_)
 
 4.2.1 (2020-02-17)
 ~~~~~~~~~~~~~~~~~~

platformio/commands/test/processor.py

@@ -83,6 +83,7 @@ class TestProcessorBase(object):
         self._outputcpp_generated = False
 
     def get_transport(self):
+        transport = None
         if self.env_options.get("platform") == "native":
             transport = "native"
         elif "framework" in self.env_options:
@@ -91,7 +92,9 @@ class TestProcessorBase(object):
             transport = self.env_options["test_transport"]
         if transport not in TRANSPORT_OPTIONS:
             raise exception.PlatformioException(
-                "Unknown Unit Test transport `%s`" % transport
+                "Unknown Unit Test transport `%s`. Please check a documentation how "
+                "to create an own 'Test Transport':\n"
+                "- https://docs.platformio.org/page/plus/unit-testing.html" % transport
             )
         return transport.lower()