[CI] Issue directions to install pytest when missing

test/python/runCythonTests.py

@@ -25,12 +25,22 @@
 CANTERA_ROOT = Path(__file__).parents[2]
 os.chdir(str(CANTERA_ROOT / "test" / "work"))
 
-import pytest
+try:
+    import pytest
+except ImportError:
+    pytest = None
 import cantera
 import cantera.test
 
 
 if __name__ == "__main__":
+    if pytest is None:
+        print("\n* ERROR: The Cantera Python test suite requires "
+            "the Python package 'pytest'.")
+        print("* ERROR: Use pip or conda to install 'pytest', "
+            "which will enable this feature.")
+        sys.exit(1)
+
     print("\n* INFO: using Cantera module found at this location:")
     print(f"*       '{cantera.__file__}'")
     print(f"* INFO: Cantera version: {cantera.__version__}")