The `assertRaises()` method is primarily used in Python's `unittest` framework...

The assertRaises() method is primarily used in Python's unittest framework to test if a specific exception is raised during the execution of a block of code. It's used to verify that expected errors occur under particular conditions, ensuring the code behaves as intended when faced with incorrect input or unexpected situations.

Syntax:

assertRaises(exception, callable, *args, **kwargs)

or used as a context manager:

with self.assertRaises(exception):
    # Code that should raise the exception

How it works:

1. First form:

   • You provide the exception type you're expecting (exception).
   • You also provide the callable (e.g., a function or method) and its arguments (*args, **kwargs).
   • If the callable raises the given exception, the test passes. If no exception or a different type of exception is raised, the test fails.

2. Second form (context manager):

   • You use a with statement to wrap the code that is supposed to raise the exception.
   • If the wrapped code raises the expected exception, the test passes. Otherwise, the test fails.

Example 1 - Using AssertRaises with Function:

import unittest

def divide(x, y):
    return x / y

class TestMath(unittest.TestCase):
    def test_divide_by_zero(self):
        self.assertRaises(ZeroDivisionError, divide, 10, 0)

Here, the test checks if dividing by zero raises a ZeroDivisionError.

Example 2 - Using AssertRaises as a Context Manager:

import unittest

class TestMath(unittest.TestCase):
    def test_list_index_error(self):
        with self.assertRaises(IndexError):
            my_list = [1, 2, 3]
            _ = my_list[5]

In this case, the test verifies that accessing an invalid index in a list raises an IndexError.

Summary:

• assertRaises() is a useful way to test that a particular exception is correctly raised during execution.
• It ensures that the code properly handles exceptional cases and invalid operations.