Fixed an issue when Unit Testing engine fails with a custom project configuration file // Resolve #3583

HISTORY.rst

@@ -66,7 +66,8 @@ PlatformIO Core 4
   - Updated PIO Unit Testing support for Mbed framework. Added compatibility with Mbed OS 6
   - Do not generate ".travis.yml" for a new project, let the user have a choice
   - Do not escape compiler arguments in VSCode template on Windows
-  - Fixed an issue with PIO Unit Testing when running multiple environments (`issue #3523 <https://github.com/platformio/platformio-core/issues/3523>`_)
+  - Fixed an issue with Unit Testing engine when running multiple environments (`issue #3523 < https://github.com/platformio/platformio-core/issues/3523>`_)
+  - Fixed an issue when Unit Testing engine fails with a custom project configuration file (`issue #3583 <https://github.com/platformio/platformio-core/issues/3583>`_)
 
 4.3.4 (2020-05-23)
 ~~~~~~~~~~~~~~~~~~

platformio/commands/test/processor.py

@@ -138,6 +138,7 @@ class TestProcessorBase(object):
             return self.cmd_ctx.invoke(
                 cmd_run,
                 project_dir=self.options["project_dir"],
+                project_conf=self.options["project_config"].path,
                 upload_port=self.options["upload_port"],
                 verbose=self.options["verbose"],
                 silent=self.options["silent"],