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Python Python Testing Be Assertive assertRaises

Didn't find a test for `get_anagrams()` using `self.assertRaises()` and an empty string

I didn't really understand assertRaises...

Can someone explain to me how this whole darn thing works? Thanks.

~Alex

tests.py
import unittest

from string_fun import get_anagrams


class AnagramTestCase(unittest.TestCase):
    def test_empty_string(self):
        get_anagrams('')
        self.assertRaises(ValueError)
string_fun.py
import itertools


def is_palindrome(yarn):
    """Return whether or not a string is a palindrome.

    A palindrome is a word/phrase that's the same in
    both directions.
    """
    return yarn == yarn[::-1]


def get_anagrams(*yarn):
    """Return a list of anagrams for a string."""
    # If only one letter came in, return it
    if yarn:
        if len(yarn[0]) == 1:
            return list(yarn)
        elif len(yarn[0] == 0):
            raise ValueError("Must provide at least two letters")
    else:
        raise ValueError("Must provide at least two letters")

    # Get all of the words from the dictionary
    words = set([
        w.strip().lower() for w in open('words.txt')
    ])

    output = set()
    for thread in yarn:
        thread = thread.lower()
        # Find all possible anagrams
        for i in range(2, len(thread)):
            fibers = set(
                [''.join(w) for w in itertools.permutations(thread, i)]
            )
            output.update(fibers.intersection(words))

    # Finally, return all of the combinations that are in the dictionary
    return sorted(list(output))

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,030 Points

You are very close. assertRaises should be used in a with block to properly handle the raised error:

class AnagramTestCase(unittest.TestCase):
    def test_empty_string(self):
        with self.assertRaises(ValueError):
            get_anagrams('')

I still don't understand how that code works, though...

Shouldn't it be running the error code first and then checking and see if that caused an error? It is just extremely confusing for me.