append locally installed packages to PYTHON_PATH for tests

tests/__init__.py

+import sys
+import os
+
+PYTHON_VERSION = sys.version_info
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+PLUGIN_ROOT_DIR = os.path.realpath(os.path.abspath(os.path.join(SCRIPT_DIR, '..')))
+PACKAGES_INSTALL_DIR = os.path.join(PLUGIN_ROOT_DIR, f'python{PYTHON_VERSION.major}.{PYTHON_VERSION.minor}')
+
+sys.path.append(PACKAGES_INSTALL_DIR)  # TODO: check for a less intrusive way to do this