assert_raises() from nose.tools won't work right

Question

I'm halfway through the book Learn Python the Hard Way by Zed Shaw. The book doesn't have any coverage or documentation for the function assert_raises().

So I tried to run this test:

from nose.tools import *
from ex48.parser import *

def test_except():
    raw_sentence = [('stop', 'the'), ('noun', 'bear'), ('verb', 'kill')]
    assert_raises(ParserError, parse_sentence(raw_sentence))

Here's the error when I tried to run nosetests:

======================================================================
ERROR: tests.parser_tests.test_except
----------------------------------------------------------------------
Traceback (most recent call last):
  File "####/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "####/ex48/tests/parser_tests.py", line 8, in test_except
    assert_raises(ParserError, parse_sentence(raw_sentence))
  File "####/ex48/ex48/parser.py", line 69, in parse_sentence
    obj = parse_object(word_list)
  File "####/ex48/ex48/parser.py", line 53, in parse_object
    raise ParserError("Expected a noun or direction next.")
 ParserError: Expected a noun or direction next.

 ----------------------------------------------------------------------
 Ran 8 tests in 0.008s

 FAILED (errors=1)

Here is where the exception is coming from:

def parse_verb(word_list):
    skip(word_list, 'stop')

    if peek(word_list) == 'verb':
       return match(word_list, 'verb')
    else:
       raise ParserError("Expected a verb next.")

The call to parse_sentence(raw_sentence) is expected to fail. The assert_raises() should work properly, but it doesn't catch the raised exception from parse_verb() yielding a failed test. What do you think is/are the problem/s?

score 0 · Accepted Answer · edited May 23 '17 at 11:33

0

Do not call parse_sentence() directly. Instead, pass it as an argument.

assert_raises(ParserError, parse_sentence, raw_sentence)

Even better, use assert_raises() in a with block. See How to use nose's assert_raises?

edited May 23 '17 at 11:33

Community

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answered May 21 '17 at 07:16

Jim K

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score 0 · Answer 2 · edited Mar 08 '19 at 01:13

0

This will work

assert_raises(ParserError, parse_verb, raw_sentence)

edited Mar 08 '19 at 01:13

Trent

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answered Mar 08 '19 at 00:02

Kaushik Pal

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assert_raises() from nose.tools won't work right

2 Answers2