TST: check that unknown occupancy defaults to 1

Some CIF files may give "?", i.e., unknown occupancy.

Author: pavoljuhas

src/diffpy/structure/tests/testdata/TeI-unkocc.cif

@@ -0,0 +1,37 @@
+data_TeI
+_audit_creation_date            2011-02-15
+
+_symmetry_space_group_name_H-M  'C 1 2/m 1'
+
+_cell_length_a                  15.383
+_cell_length_b                  4.182
+_cell_length_c                  11.999
+_cell_angle_alpha               90
+_cell_angle_beta                128.09
+_cell_angle_gamma               90
+
+loop_
+  _atom_site_label
+  _atom_site_type_symbol
+  _atom_site_fract_x
+  _atom_site_fract_y
+  _atom_site_fract_z
+  _atom_site_U_iso_or_equiv
+  _atom_site_adp_type
+  _atom_site_occupancy
+  Te1   Te1+   0.306590    0.000000    0.185920    0.019227 Uani  ?
+  Te2   Te1+   0.429170    0.500000    0.168170    0.019784 Uani  ?
+  I1    I1-    0.153740    0.500000    0.182510    0.024813 Uani  ?
+  I2    I1-    0.610730    0.500000    0.448390    0.026878 Uani  ?
+loop_
+  _atom_site_aniso_label
+  _atom_site_aniso_U_11
+  _atom_site_aniso_U_22
+  _atom_site_aniso_U_33
+  _atom_site_aniso_U_12
+  _atom_site_aniso_U_13
+  _atom_site_aniso_U_23
+  Te1    0.021100  0.019500  0.016000  0.000000  0.010900  0.000000
+  Te2    0.022300  0.018000  0.025400  0.000000  0.017900  0.000000
+  I1     0.025000  0.023400  0.034500  0.000000  0.022600  0.000000
+  I2     0.023400  0.029500  0.025300  0.000000  0.013800  0.000000

src/diffpy/structure/tests/testp_cif.py

@@ -249,6 +249,13 @@ def test_eps(self):
         return
 
 
+    def test_unknown_occupancy(self):
+        "test CIF file with unknown occupancy data"
+        stru = self.ptest.parseFile(datafile('TeI-unkocc.cif'))
+        self.assertTrue(numpy.array_equal(16 * [1], stru.occupancy))
+        return
+
+
     def test_nosites_cif(self):
         """Test reading of CIF file with no valid sites.
         """