nodev.specs helps you write robust tests that describe the abstract behaviour of your code leaving many implementation details out of your tests.

The general idea is best explained with an example, let’s write a specification test for the following function skip_comments that returns the non-comment part of every line in the input file:

def skip_comments(stream):
    return [line.partition('#')[0] for line in stream]

The simplest unit test may look like the following:

def test_skip_comments():
    assert skip_comments(['# comment']) == ['']
    assert skip_comments(['value # comment']) == ['value ']
    assert skip_comments(['value 1', '', 'value 2']) == ['value 1', '', value 2']

Such a unit test is much more tied to current skip_comments implementation than it needs to be and the test will need update every time a tiny feature is added, like turning the function into a generator:

def skip_comments(stream):
    for line in stream:
        yield line.partition('#')[0]

This can be fixed by re-writing the test in more generic way:

def test_skip_comments():
    assert '' in skip_comments(['# comment'])
    assert 'value ' in skip_comments(['value # comment'])
    assert 'value 1' in skip_comments(['value 1', '', 'value 2'])
    assert 'value 2' in skip_comments(['value 1', '', 'value 2'])

Let’s re-write the test making use of the nodev.specs.FlatContainer helper:

def test_skip_comments():
    assert '' in FlatContainer(skip_comments(['# comment']))
    assert 'value ' in FlatContainer(skip_comments(['value # comment']))
    assert 'value 1' in FlatContainer(skip_comments(['value 1', '', 'value 2']))
    assert 'value 2' in FlatContainer(skip_comments(['value 1', '', 'value 2']))

Now you can choose to skip empty lines returning the current line index instead:

def skip_comments(stream):
    for index, line in enumerate(stream):
        value = line.partition('#')[0]
        if value:
            yield index, value

Or return also the comment for every line:

def skip_comments(stream):
    for index, line in enumerate(stream):
        value, sep, comment = line.partition('#')
        if value:
            yield index, value, sep + comment

The nodev test needs no update because it makes almost no assumption on the details of the return value.

Project resources

Support	https://stackoverflow.com/search?q=nodev
Development	https://github.com/nodev-io/nodev.specs
Discussion	To be decided, see issue #15 of the pytest-nodev repository.
Download	https://pypi.python.org/pypi/nodev.specs
Code quality
nodev website	http://nodev.io