mock_open doesn't present a consistent filesystem

[GoogleCodeExporter]

mock.mock_open doesn't work well for even simple tests involving files, because 
you can't read what you've written.

I'm trying to write a near-trivial test of a function that reads a file and 
appends to it, but of course it doesn't work because the state of the "mock 
filesystem" never changes.

Sample code.

import mock
o = mock.mock_open()
mock_open = mock.mock_open()
with mock_open('/tmp/test.txt', 'w') as f:
  f.write('hello')

with mock_open('/tmp/test.txt', 'r') as f:
  assert f.read() == 'hello'

Original issue reported on code.google.com by tom.ritc...@gmail.com on 3 Oct 2012 at 8:48

[GoogleCodeExporter]

You are of course correct, mock objects do not implement file *behaviour*. For 
mocking out a whole filesystem some objects more complex than "dumb" mock 
objects are needed. There are projects that provide in memory filesystem apis - 
you could use patch (or dependency injection) to put these in place for your 
tests.

Alternatively, if you want the behaviour in mock and it can be implemented 
*simply* then I would consider a patch.

Original comment by fuzzyman on 4 Oct 2012 at 10:43

• Added labels: Type-Enhancement
• Removed labels: Type-Defect

[GoogleCodeExporter]

Thanks, I'll tinker with this as time permits and report back when I have 
something for you!

Original comment by tom.ritc...@gmail.com on 4 Oct 2012 at 4:08

• Added labels: ****
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