Set PROJECT_DIR variable for unittest tests.

Author: MartinPavella

backends/nxp/tests/config.py

@@ -15,6 +15,10 @@
 # TODO(Robert Kalmar) In accordance with the "TODO(dbort): Prune /test[s]/ dirs, /third-party/ dirs" in pyproject.toml,
 #  once the test folders are not installed we can derive the path from current file location: `pathlib.Path(__file__)`
 PROJECT_DIR = os.environ.get("PROJECT_DIR")
+if not PROJECT_DIR:
+    # Auto-detect: The PROJECT_DIR env variable is set by the conftest.py in backends.nxp.tests.conftest. But unittests
+    #               don't use the conftest, so this variable is not set -> set it manually here in that case.
+    PROJECT_DIR = str(pathlib.Path(__file__).parent.parent.parent.parent)
 assert PROJECT_DIR and os.path.exists(
     PROJECT_DIR
 ), f"Invalid PROJECT_DIR env variable: `{PROJECT_DIR}`."