"This method is used by default when comparing strings with assertEqual()." https://docs.python.org/2/library/unittest.html?highlight=unittest#unittest.TestCase.assertMultiLineEqual

asserttest.py

import unittest

class AssertTests(unittest.TestCase):
    def testAssertEqual(self):
        self.assertEqual('ABCD', 'ABC')

    def testAssertMultiLineEqual(self):
        self.assertMultiLineEqual('ABCD', 'ABC')

if __name__ == '__main__':
    unittest.main()

''' # OUTPUT

$ python2.7 asserttest.py
FF
======================================================================
FAIL: test_one (__main__.AssertTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "asserttest.py", line 6, in test_one
    self.assertEqual('ABCD', 'ABC')
AssertionError: 'ABCD' != 'ABC'

======================================================================
FAIL: test_transcribes_all_occurences (__main__.AssertTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "asserttest.py", line 9, in test_transcribes_all_occurences
    self.assertMultiLineEqual('ABCD', 'ABC')
AssertionError: 'ABCD' != 'ABC'
- ABCD
?    -
+ ABC


----------------------------------------------------------------------
Ran 2 tests in 0.001s

FAILED (failures=2)


$ python3.5 asserttest.py
FF
======================================================================
FAIL: test_one (__main__.AssertTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "asserttest.py", line 6, in test_one
    self.assertEqual('ABCD', 'ABC')
AssertionError: 'ABCD' != 'ABC'
- ABCD
?    -
+ ABC


======================================================================
FAIL: test_transcribes_all_occurences (__main__.AssertTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "asserttest.py", line 9, in test_transcribes_all_occurences
    self.assertMultiLineEqual('ABCD', 'ABC')
AssertionError: 'ABCD' != 'ABC'
- ABCD
?    -
+ ABC


----------------------------------------------------------------------
Ran 2 tests in 0.001s

FAILED (failures=2)
'''