Mock 'python --version' command

tests/test_xfel_calibrate/conftest.py

@@ -48,6 +48,10 @@ class FakeProcessCalibrate(FakeProcess):
         self.register_subprocess(
             [self.any(), '-m', 'pip', 'freeze'], stdout=["h5py==3.3.0"],
         )
+        # For getting Python version from user venv
+        self.register_subprocess(
+            [self.any(), '--version'], stdout=["Python 3.x.y"]
+        )
 
         self.keep_last_process(True)