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Python unittest – assertIn() function

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  • Last Updated : 29 Aug, 2020
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assertIn() in Python is a unittest library function that is used in unit testing to check whether a string is contained in other or not. This function will take three string parameters as input and return a boolean value depending upon the assert condition. If the key is contained in container string it will return true else it returns false.

Syntax: assertIn(key, container, message)

Parameters: assertIn() accept three parameters which are listed below with explanation:

  • key:  a string whose presence is checked in the given container
  • container: a string in which key string is searched
  • message: a string sentence as a message which got displayed when the test case got failed.

Listed below are two different examples illustrating the positive and negative test case for given assert function:

Example 1: Negative Test case

Python3




# test suite
import unittest
  
class TestStringMethods(unittest.TestCase):
    # test function to test whether key is present in container
    def test_negative(self):
        key = "gfg"
        container = "geeksforgeeks"
        # error message in case if test case got failed
        message = "key is not in container."
        # assertIn() to check if key is in container
        self.assertIn(key, container, message)
  
if __name__ == '__main__':
    unittest.main()

Output:

F
======================================================================
FAIL: test_negative (__main__.TestStringMethods)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/e920f2cd9195a3fd72bd531f7f101754.py", line 12, in test_negative
    self.assertIn(key, container, message)
AssertionError: 'gfg' not found in 'geeksforgeeks' : key is not in container.

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)

Example 2: Positive Test case

Python3




# test suite
import unittest
  
  
class TestStringMethods(unittest.TestCase):
    # test function to test whether key is present in container
    def test_positive(self):
        key = "geeks"
        container = "geeksforgeeks"
        # error message in case if test case got failed
        message = "key is not in container."
        # assertIn() to check if key is in container
        self.assertIn(key, container, message)
  
  
if __name__ == '__main__':
    unittest.main()

Output:

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

Reference: https://docs.python.org/3/library/unittest.html


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