How to prevent truncation of a string in a python unit test
I am doing a unit test in python for my program and I would like to do an assertEquals test.
My code looks something like this:
class UnitTest(unittest.TestCase):
def test_parser(self):
self.assertEquals(parser,"some long string", "String is not equal")
However, since my string is too long, I got something like testing [471 characters] 0! = Testing [473 characters]. I want to see exactly what the difference is between the two lines, not see truncated.
Anyone have an idea how to counter this problem?
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unittest.TestCase.assertEquals
tries to give you the actual line difference while making the text fit on your screen.
To do this, it truncates shared sections, so sections that do not have differences are truncated by replacing them with [<count> chars]
chunks:
>>> case.assertEqual('foo' * 200, 'foo' * 100 + 'bar' + 'foo' * 99)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 821, in assertEqual
assertion_func(first, second, msg=msg)
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 1194, in assertMultiLineEqual
self.fail(self._formatMessage(msg, standardMsg))
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 666, in fail
raise self.failureException(msg)
AssertionError: 'foof[291 chars]oofoofoofoofoofoofoofoofoofoofoofoofoofoofoofo[255 chars]ofoo' != 'foof[291 chars]oofoobarfoofoofoofoofoofoofoofoofoofoofoofoofo[255 chars]ofoo'
Diff is 1819 characters long. Set self.maxDiff to None to see it.
In the above example, the two strings have a long prefix that has been shortened by replacing 291 characters with [291 chars]
in both prefixes. They also have a long postfix that is shortened again in both places, replacing the text with [255 chars]
.
The actual difference is still displayed, right in the middle.
Of course, when you make this difference too long, then even the difference is truncated:
>>> case.assertEqual('foo' * 200, 'foo' * 80 + 'bar' * 30 + 'foo' * 80)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 821, in assertEqual
assertion_func(first, second, msg=msg)
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 1194, in assertMultiLineEqual
self.fail(self._formatMessage(msg, standardMsg))
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 666, in fail
raise self.failureException(msg)
AssertionError: 'foof[231 chars]oofoofoofoofoofoofoofoofoofoofoofoofoofoofoofo[315 chars]ofoo' != 'foof[231 chars]oofoobarbarbarbarbarbarbarbarbarbarbarbarbarba[285 chars]ofoo'
Diff is 1873 characters long. Set self.maxDiff to None to see it.
This is where the general postfix starts to differ, but the beginning of the difference is still visible and should help you figure out where the text went wrong.
If that's not enough, you can either increase or eliminate the difference limits. Set the TestCase.maxDiff
attribute to a larger number (default 8 * 80, 80 lines of text) or set it to None
completely eliminate:
self.maxDiff = None
Note that if your line does not contain newlines, that diff may be unreadable:
AssertionError: 'foof [231 chars] oofoofoofoofoofoofoofoofoofoofoofoofoofoofo [315 characters] ofoo'! = 'Foof [231 characters] oofoobarbarbarbarbarbarbarbarbarbarbarba [285 CHARS] ofoo "-?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^ +?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
In this case, it may be more useful to wrap your input and output texts:
from textwrap import wrap
self.maxDiff = None
self.assertEquals(wrap(parser), wrap("some long string"), "String is not equal")
so you get a better and more readable diff output:
>>> from textwrap import wrap
>>> case.assertEqual(wrap('foo' * 200), wrap('foo' * 80 + 'bar' * 30 + 'foo' * 80))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 821, in assertEqual
assertion_func(first, second, msg=msg)
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 1019, in assertListEqual
self.assertSequenceEqual(list1, list2, msg, seq_type=list)
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 1001, in assertSequenceEqual
self.fail(msg)
File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/case.py", line 666, in fail
raise self.failureException(msg)
AssertionError: Lists differ: ['foo[244 chars]oofoofoofoofoofoofoofoofoofoofoofoofoofoofoof'[336 chars]foo'] != ['foo[244 chars]oofoobarbarbarbarbarbarbarbarbarbarbarbarbarb'[306 chars]foo']
First differing element 3:
'foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoof'
'foofoofoofoofoofoofoofoofoofoobarbarbarbarbarbarbarbarbarbarbarbarbarb'
['foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoof',
'oofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofo',
'ofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoo',
- 'foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoof',
- 'oofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofo',
+ 'foofoofoofoofoofoofoofoofoofoobarbarbarbarbarbarbarbarbarbarbarbarbarb',
+ 'arbarbarbarbarbarbarbarbarbarbarbarbarbarbarbarbarfoofoofoofoofoofoofo',
'ofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoo',
'foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoof',
'oofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoofo',
- 'ofoofoofoofoofoofoofoofoofoofoofoofoofoo']
+ 'ofoofoofoo']
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