Remove the use of extra variable for params to prevent global scope in the file

Author: bobleesj

tests/conftest.py

@@ -46,3 +46,11 @@ def wavelength_warning_msg():
         "To specify a wavelength, if you have do = DiffractionObject(xarray, yarray, 'tth'), "
         "you may set do.wavelength = 1.54 for a wavelength of 1.54 angstroms."
     )
+
+
+@pytest.fixture
+def invalid_q_or_d_or_wavelength_error_msg():
+    return (
+        "The supplied input array and wavelength will result in an impossible two-theta. "
+        "Please check these values and re-instantiate the DiffractionObject with correct values."
+    )