assertIsInstance() in Python is a unittest library function that is used in unit testing to check whether an object is an instance of a given class or not. This function will take three parameters as input and return a boolean value depending upon the assert condition. If the object is an instance ofthe given class it will return true else it returns false.
Syntax: assertIsInstance(object, className, message)
Parameters: assertIsInstance() accept three parameters which are listed below with explanation:
- object: Object which is checked as an instance of the given class
- className: Class name to be compared for object instance
- 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 # test class class Myclass: x = 5 class Myclass2: x = 6 class TestClass(unittest.TestCase): # test function to test whether obj is instance of class def test_negative(self): objectName = Myclass() # error message in case if test case got failed message = "given object is not instance of Myclass." # assertIsInstance() to check if obj is instance of class self.assertIsInstance(objectName, Myclass2, message) if __name__ == '__main__': unittest.main() |
Output:
F
======================================================================
FAIL: test_negative (__main__.TestStringMethods)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/a2e9f97d79f7d8c1fbd00c4df704d402.py", line 22, in test_negative
self.assertIsInstance(objectName, Myclass2, message)
AssertionError: <__main__.Myclass object at 0x7f1e9bead0b8> is not an instance of <class '__main__.Myclass2'> : given object is not instance of Myclass.
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)
Example 2: Positive Test case
Python3
# test suite import unittest # test class class Myclass: x = 5 class TestClass(unittest.TestCase): # test function to test whether obj is instance of class def test_positive(self): objectName = Myclass() # error message in case if test case got failed message = "given object is not instance of Myclass." # assertIsInstance() to check if obj is instance of class self.assertIsInstance(objectName, Myclass, message) if __name__ == '__main__': unittest.main() |
Output:
. ---------------------------------------------------------------------- Ran 1 test in 0.000s OK
Reference: https://docs.python.org/3/library/unittest.html
