TST: cover processing of CIF-defined space group

Test this on dummy CIF file with non-standard SG.

Author: pavoljuhas

src/diffpy/structure/tests/testdata/customsg.cif

@@ -0,0 +1,44 @@
+data_9008569
+_chemical_name 'Graphite'
+loop_
+_publ_author_name
+'Wyckoff R W G'
+_journal_name_full "Crystal Structures"
+_journal_volume 1
+_journal_year 1963
+_journal_page_first 7
+_journal_page_last 83
+_publ_section_title
+;
+ Second edition. Interscience Publishers, New York, New York
+;
+_chemical_formula_sum 'C'
+_cell_length_a 2.456
+_cell_length_b 2.456
+_cell_length_c 6.696
+_cell_angle_alpha 90
+_cell_angle_beta 90
+_cell_angle_gamma 120
+_cell_volume 34.979
+# _symmetry_space_group_name_H-M 'P 63 m c'
+loop_
+_symmetry_equiv_pos_as_xyz
+  'x,y,z'
+  '-x,-x+y,1/2+z'
+  'x-y,x,1/2+z'
+  '-y,-x,z'
+  '-y,x-y,z'
+  'x-y,-y,1/2+z'
+# '-x,-y,1/2+z'
+# 'x,x-y,z'
+# '-x+y,-x,z'
+# 'y,x,1/2+z'
+# 'y,-x+y,1/2+z'
+# '-x+y,y,z'
+loop_
+_atom_site_label
+_atom_site_fract_x
+_atom_site_fract_y
+_atom_site_fract_z
+C1   0.00000   0.00000   0.00000
+C2   0.33333   0.66667   0.00000

src/diffpy/structure/tests/testp_cif.py

@@ -277,6 +277,18 @@ def test_badspacegroup_cif(self):
         return
 
 
+    def test_custom_spacegroup_cif(self):
+        """Test parsing of nonstandard symops-defined space group.
+        """
+        pfile = self.pfile
+        filename = datafile('customsg.cif')
+        pfile.parseFile(filename)
+        sg = pfile.spacegroup
+        self.assertEqual('CIF data', sg.short_name)
+        self.assertEqual(6, len(sg.symop_list))
+        return
+
+
     def test_getParser(self):
         """Test passing of eps keyword argument by getParser function.
         """