Is there any way to check with Python unittest assert if an iterable is not empty?

Question

After submitting queries to a service, I get a dictionary / a list back and I want to make sure it's not empty. I am on Python 2.7.

I am surprised I don't see any assertEmpty method for the unittest.TestCase class instance.

The existing alternatives such as:

self.assertTrue(bool(d))

and

self.assertNotEqual(d,{})

and

self.assertGreater(len(d),0)

just don't look right.

Is this kind of method is missing in the Python unittest framework? If yes, what would be the most pythonic way to assert that an iterable is not empty?

Answer 1

Empty lists/dicts evaluate to False, so self.assertTrue(d) gets the job done.

Answer 2

Depends exactly what you are looking for.

If you want to make sure the object is an iterable and it is not empty:

# TypeError: object of type 'NoneType' has no len()
# if my_iterable is None
self.assertTrue(len(my_iterable))

If it is OK for the object being tested to be None:

self.assertTrue(my_maybe_iterable)

Answer 3

As @gplayer already mentioned: it's possible to check for non emptiness with assertTrue() (and vice versa with assertFalse() for emptiness of course).

But, like @Alex Tereshenkov previously has pointed out in the comments, all those assertTrue() and assertFalse() method calls clutter the code and are kind of misleading because we wanted to check for emptiness.

So in the sake of cleaner code we can define our own assertEmpty() and assertNotEmpty() methods:

def assertEmpty(self, obj):
    self.assertFalse(obj)

def assertNotEmpty(self, obj):
    self.assertTrue(obj)

Answer 4

Maybe:

self.assertRaises(StopIteration, next(iterable_object))

Answer 5

All the credit for this goes to winklerrr, I am just extending his idea: have importable mixins for when you need assertEmpty or assertNotEmpty:

class AssertEmptyMixin( object ):
    def assertEmpty(self, obj):
        self.assertFalse(obj)

class AssertNotEmptyMixin( object ):
    def assertNotEmpty(self, obj):
        self.assertTrue(obj)

Caveat, mixins should go on the left:

class MyThoroughTests( AssertNotEmptyMixin, TestCase ):
    def test_my_code( self ):
        ...
        self.assertNotEmpty( something )