Collgrid.py.test.in: add option -O

test/pytest/Collgrid.py.test.in

@@ -22,7 +22,7 @@ for GRIDTYPE in GRIDTYPES:
 
             t = TAPTest(f'{GRIDTYPE} {DIST}')
             t.add(f'{CDO} distgrid,{DIST} {IFILE} xxx')
-            t.add(f'{CDO} {OPERATOR}{argument} xxx* {OFILE}')
+            t.add(f'{CDO} -O {OPERATOR}{argument} xxx* {OFILE}')
             t.add(f'{CDO} diff {IFILE} {OFILE}')
             t.clean(OFILE, "xxx*")
             test_module.add(t)