test-revert: add case where file exists neither in "base" nor in "parent"

tests/test-revert.t

@@ -443,6 +443,8 b' Write the python script to disk'
   >     'added': [None, 'parent'],
   >     # removed: file exist in base but is removed from parent
   >     'removed': ['base', None],
+  >     # file exist neither in base not in parent
+  >     'missing': [None, None],
   > }
   > 
   > # content of file in working copy
@@ -495,6 +497,7 b' check list of planned files'
   $ python gen-revert-cases.py filelist
   added_clean
   clean_clean
+  missing_clean
   modified_clean
   removed_clean
 
@@ -650,6 +653,9 b' revert all files individually and check '
   ### revert for: clean_clean
   no changes needed to clean_clean
   
+  ### revert for: missing_clean
+  missing_clean: no such file in rev * (glob)
+  
   ### revert for: modified_clean
   no changes needed to modified_clean
   
@@ -691,6 +697,9 b' Misbehavior:'
   
   ### revert for: clean_clean
   
+  ### revert for: missing_clean
+  missing_clean: no such file in rev * (glob)
+  
   ### revert for: modified_clean
   
   ### revert for: removed_clean