how to handle Exceptions (Errors): tests and solutions

Exception Handling in tests

Exception Handling in tests: tests

The code in exceptions/tests/test_exceptions.py from how to test that an Exception is raised

exceptions/tests/test_exceptions.py
 1import src.exceptions
 2import unittest
 3
 4
 5class TestExceptions(unittest.TestCase):
 6
 7    @staticmethod
 8    def assert_raises(code, exception):
 9        try:
10            exec(code)
11        except exception:
12            pass
13        else:
14            raise AssertionError
15
16    def test_catching_module_not_found_error(self):
17        self.assert_raises(
18            'import does_not_exist', ModuleNotFoundError
19        )
20        with self.assertRaises(ModuleNotFoundError):
21            import does_not_exist
exceptions/tests/test_exceptions.py
23    def test_catching_name_error(self):
24        self.assert_raises('not_defined', NameError)
25        with self.assertRaises(NameError):
26            not_defined
27
28    def test_catching_attribute_error(self):
29        self.assert_raises(
30            'src.exceptions.does_not_exist', AttributeError
31        )
32        with self.assertRaises(AttributeError):
33            src.exceptions.does_not_exist
34
35    def test_catching_type_error(self):
36        self.assert_raises(
37            "src.exceptions.function_name('the input')",
38            TypeError
39        )
40        with self.assertRaises(TypeError):
41            src.exceptions.function_name('the input')
exceptions/tests/test_exceptions.py
43    def test_catching_index_error(self):
44        self.assert_raises("'a string'[8]", IndexError)
45        self.assert_raises("'a string'[-9]", IndexError)
46
47        with self.assertRaises(IndexError):
48            'a string'[8]
49        with self.assertRaises(IndexError):
50            'a string'[-9]
51
52        self.assert_raises(
53            "(0, 1, 2, 'n')[100]", IndexError
54        )
55        self.assert_raises(
56            "(0, 1, 2, 'n')[-100]", IndexError
57        )
58
59        with self.assertRaises(IndexError):
60            (0, 1, 2, 'n')[100]
61        with self.assertRaises(IndexError):
62            (0, 1, 2, 'n')[-100]
exceptions/tests/test_exceptions.py
64    def test_catching_key_error(self):
65        self.assert_raises(
66            "{'key': 'value'}['not_in_dictionary']",
67            KeyError
68        )
69        with self.assertRaises(KeyError):
70            {'key': 'value'}['not_in_dictionary']
71
72    def test_catching_zero_division_error(self):
73        self.assert_raises('1 / 0', ZeroDivisionError)
74        with self.assertRaises(ZeroDivisionError):
75            1 / 0
76
77    def test_catching_exceptions(self):
78        self.assert_raises('raise Exception', Exception)
79        with self.assertRaises(Exception):
80            raise Exception
81
82
83# Exceptions seen
84# AssertionError
85# ModuleNotFoundError
86# NameError
87# AttributeError
88# TypeError
89# SyntaxError
90# IndexError
91# KeyError
92# ZeroDivisionError

Exception Handling in tests: solution

The code in src/exceptions/__init__.py from how to test that an Exception is raised

exceptions/src/exceptions/__init__.py
1def function_name():
2    return None

Exception Handling in programs tests and solutions

Exception Handling in programs: tests

The code in exceptions/tests/test_exceptions.py from how to handle Exceptions in programs

exceptions/tests/test_exceptions.py
 1import src.exceptions
 2import unittest
 3
 4
 5class TestExceptions(unittest.TestCase):
 6
 7    @staticmethod
 8    def assert_raises(code, exception):
 9        try:
10            exec(code)
11        except exception:
12            pass
13        else:
14            raise AssertionError(f'{exception} not raised')
15
16    def test_catching_module_not_found_error(self):
17        self.assert_raises(
18            'import does_not_exist', ModuleNotFoundError
19        )
20        with self.assertRaises(ModuleNotFoundError):
21            import does_not_exist
exceptions/tests/test_exceptions.py
23    def test_catching_name_error(self):
24        self.assert_raises('not_defined', NameError)
25        with self.assertRaises(NameError):
26            not_defined
27
28    def test_catching_attribute_error(self):
29        self.assert_raises(
30            'src.exceptions.does_not_exist', AttributeError
31        )
32        with self.assertRaises(AttributeError):
33            src.exceptions.does_not_exist
34
35    def test_catching_type_error(self):
36        self.assert_raises(
37            "src.exceptions.function_name('the input')",
38            TypeError
39        )
40        with self.assertRaises(TypeError):
41            src.exceptions.function_name('the input')
exceptions/tests/test_exceptions.py
43    def test_catching_index_error(self):
44        self.assert_raises("'a string'[8]", IndexError)
45        self.assert_raises("'a string'[-9]", IndexError)
46
47        with self.assertRaises(IndexError):
48            'a string'[8]
49        with self.assertRaises(IndexError):
50            'a string'[-9]
51
52        self.assert_raises(
53            "(0, 1, 2, 'n')[100]", IndexError
54        )
55        self.assert_raises(
56            "(0, 1, 2, 'n')[-100]", IndexError
57        )
58
59        with self.assertRaises(IndexError):
60            (0, 1, 2, 'n')[100]
61        with self.assertRaises(IndexError):
62            (0, 1, 2, 'n')[-100]
exceptions/tests/test_exceptions.py
64    def test_catching_key_error(self):
65        self.assert_raises(
66            "{'key': 'value'}['not_in_dictionary']",
67            KeyError
68        )
69        with self.assertRaises(KeyError):
70            {'key': 'value'}['not_in_dictionary']
71
72    def test_catching_zero_division_error(self):
73        self.assert_raises('1 / 0', ZeroDivisionError)
74        with self.assertRaises(ZeroDivisionError):
75            1 / 0
76
77    def test_catching_exceptions(self):
78        self.assert_raises('raise Exception', Exception)
79        with self.assertRaises(Exception):
80            raise Exception
81
82    def test_catching_exceptions_w_messages(self):
83        with self.assertRaisesRegex(
84            Exception, 'BOOM!!!'
85        ):
86            src.exceptions.raise_exception()
exceptions/tests/test_exceptions.py
 88    def test_catching_failure(self):
 89        self.assertEqual(
 90            src.exceptions.an_exception_handler(
 91                src.exceptions.raise_exception
 92            ),
 93            'failed'
 94        )
 95
 96    def test_catching_success(self):
 97        self.assertEqual(
 98            src.exceptions.an_exception_handler(
 99                src.exceptions.function_name
100            ),
101            'succeeded'
102        )
103
104
105# Exceptions seen
106# AssertionError
107# ModuleNotFoundError
108# NameError
109# AttributeError
110# TypeError
111# SyntaxError
112# IndexError
113# KeyError
114# ZeroDivisionError

Exception Handling in programs: solutions

The code in src/exceptions/__init__.py from how to handle Exceptions in programs

exceptions/src/exceptions/__init__.py
 1def function_name():
 2    return None
 3
 4
 5def raise_exception():
 6    raise Exception('BOOM!!!')
 7
 8
 9def an_exception_handler(a_function):
10    try:
11        a_function()
12    except Exception:
13        return 'failed'
14    else:
15        return 'succeeded'