added more tests and refined help message

Author: yucongalicechen

src/diffpy/labpdfproc/labpdfprocapp.py

@@ -65,7 +65,8 @@ def get_args():
         nargs="+",
         help="Specify (multiple) key-value pairs to be loaded into metadata using the format key=value. "
         "Please separate each pair with whitespace, and make sure no whitespaces before or after the = sign. "
-        "Please avoid putting = in a key. If you repeat key names, it will replace previous values. "
+        "Avoid using = in keys. If multiple = signs are present, only the first one separates the key and value. "
+        "If you repeat key names, it will replace previous values. "
         "If a key or value contains whitespace, enclose it in quotes. "
         'For example, you can specify -u "facility=NSLS II" beamline=28ID-2 "favorite color"=blue',
     )

src/diffpy/labpdfproc/tests/test_tools.py

@@ -85,6 +85,8 @@ def test_set_wavelength_bad(inputs, msg):
         [["facility=NSLS II", "beamline=28ID-2", "favorite color=blue"]],
         [["facility", "NSLS II"], ["beamline", "28ID-2"], ["favorite color", "blue"]],
     ),
+    ([["facility=NSLS II", "facility=NSLS III"]], [["facility", "NSLS III"]]),
+    ([["x=y=z"]], [["x", "y=z"]]),
 ]