BF/ENH: assure that foo.txt exists and no conflicts for demonstration

Author: yarikoptic

command.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 importos
-
+fromos.pathimportlexists
 
 classMoveFileCommand(object):
 
@@ -28,13 +28,23 @@ def main():
 command_stack.append(MoveFileCommand('foo.txt', 'bar.txt'))
 command_stack.append(MoveFileCommand('bar.txt', 'baz.txt'))
 
-# they can be executed later on
-forcmdincommand_stack:
-cmd.execute()
-
-# and can also be undone at will
-forcmdinreversed(command_stack):
-cmd.undo()
+# verify that none of the target files exist
+assert(notlexists("foo.txt"))
+assert(notlexists("bar.txt"))
+assert(notlexists("baz.txt"))
+try:
+withopen("foo.txt", "w"): # Creating the file
+pass
+
+# they can be executed later on
+forcmdincommand_stack:
+cmd.execute()
+
+# and can also be undone at will
+forcmdinreversed(command_stack):
+cmd.undo()
+finally:
+os.unlink("foo.txt")
 
 if__name__=="__main__":
 main()