CODEWITHSUNDEEP
python
jukhamil
jukhamil

Reputation: 819

Unittest error 'issubclass arg 2'

I am not sure what the meaning of this error is. This is my test:

def test_method_delete(self):
        test_graph = trie_builder.Graph()
        node_name = 'node_0'
        test_graph.node(node_name)
        # Create a node.

        test_graph.delete(node_name)
        # Delete the node.
        self.assertNotIn(node_name, test_graph.node_list)
        node_name = 'node_1'
        with self.assertRaises(KeyError('ERROR: Attempt to delete non-existent node.')):
            test_graph.delete(node_name)

This is my method:

def delete(self, node_name):
        if node_name in self.node_list:
            del self.node_list[node_name]
        else:
            raise(KeyError('ERROR: Attempt to delete non-existent node.'))

And this is the error:

ERROR: test_method_delete (__main__.test_class_Graph)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_trie_builder.py", line 66, in test_method_delete
    test_graph.delete(node_name)
  File "/Users/juliushamilton/Documents/Work/Nantomics_trie_builder/trie_builder/trie_builder.py", line 25, in delete
    raise(KeyError('ERROR: Attempt to delete non-existent node.'))
KeyError: 'ERROR: Attempt to delete non-existent node.'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test_trie_builder.py", line 66, in test_method_delete
    test_graph.delete(node_name)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/case.py", line 184, in __exit__
    if not issubclass(exc_type, self.expected):
TypeError: issubclass() arg 2 must be a class or tuple of classes

What could be the problem? What is 'arg2' referring to?

Upvotes: 0

Views: 614

Answers (1)

zstewart
zstewart

Reputation: 2177

Have you tried passing the KeyError class (without instantiating an instance) to assertRaises? It looks like assertRaises is trying to check that the error it got is of the type of error class you gave it, but KeyError('ERROR: Attempt to delete non-existent node.') is an instance of type KeyError, not the type itself.

with self.assertRaises(KeyError):
    test_graph.delete(node_name)

It looks like the docs don't make this clear: https://docs.python.org/2/library/unittest.html#unittest.TestCase.assertRaises, but from the stack trace your gave it looks like what it does is check that the exception it receives is a subclass of the exception class you passed to it using issubclass. issubclass can only accept a type as its second argument, so passing an instance is the error you are getting.

If you want to also check the error text you need to use assertRaisesRegexp: https://docs.python.org/2/library/unittest.html#unittest.TestCase.assertRaisesRegexp

Upvotes: 2

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