[TIP] testing calls to mocked open?

[Andrew Hammond]

I've tried the approach you mention below but with no luck. My test
code now reads:

        self.mock_open.assert_called_once_with('/path/to/fake_file_name.txt',
'rb')

# TODO: figure out how to test this
#        self.mock_open.return_value.seek.assert_called_once_with(0)
#        self.mock_open.return_value.read.assert_called_once_with(1024*5)

The first assertion passes, the two commented out assertions fail.

A

On Wed, Sep 14, 2011 at 11:06 AM, Julian Berman <julian at grayvines.com> wrote:
>
> On Sep 14, 2011, at 1:23 PM, Andrew Hammond wrote:
>
>> I have the following code that I want to test:
>>
>>        with open(self.file_name, 'rb') as f:
>>            f.seek(self.last_byte_uploaded)
>>            chunk = f.read(self.chunk_size)
>>
>> Using Mock, I have patched open and the following tests work correctly:
>>
>>        k = self.mock_open.call_args_list
>>        self.assertEquals(1, len(k))
>>        self.assertEquals(('/path/to/fake_file_name.txt', 'rb'), k[0][0])
>>        self.assertEquals({}, k[0][1])
>>
>
> In case you're unaware, there's a quick way of writing your assertion using assert_called_once_with. The answer to your question (at least how I generally do it) is to do something like:
>
> mock_file = mock.Mock()
>
> with mock.patch(yourmodule, "open", create=True) as mock_open:
>    mock_open.return_value = mock_file
>    mock_open.assert_called_once_with(('/path/to/fake_file_name.txt', 'rb'))
>    mock_file.seek.assert_called_once_with(self.byte_thing)
>    mock_file.read.assert_called_once_with(whatever)
>
> You can also make mock_file have the spec of a file object if you want to be careful about that.
>
> (Mock is lovely :)
>
> Julian