Use non-interactive backend for testing

Author: bpark1327

tests/conftest.py

@@ -2,8 +2,11 @@
 from pathlib import Path
 
 import eeweather.cache as ec
+import matplotlib as mpl
 import pytest
 
+mpl.use("Agg")  # Use non-interactive backend for testing
+
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 from utils.post_process import generate_cvrmse_comparison_plot