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To make tests robust and detailed we also should check all exceptions which can occur during code execution. To write assertions about raised exceptions, you can use pytestuse pytest.raises() as  as a context manager. For this example, we are going to write a test to check if the divide() function returns an exception during a dividing number by zero or not.  In this examplecase, all tests are written in the test_exceptions.py file. For the tutorial purpose, there is also created new file list_func.py which contains the extra function to test.  

Our project folder should look like this:

.
├── code_examples
│   ├── division_func.py
│   ├── __init__.py
│   └── list_func.py
└── tests
    ├── __init__.py
    ├── test_division_func.py
    └── test_exceptions.py

ZeroDivisionError example

For the record division() function looks like this:

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To check is dividing by zero returns exception we are going to import pytest Pytest and write a test which that looks like this:

import pytest
from code_examples.division_func import division


def test_division_by_zero():
    with pytest.raises(ZeroDivisionError):
        division(1, 0)

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This test uses a special context manager facility in pytestin Pytest, in which you run a block of code that you expect to raise an exception, and let pytest handle it. Your test will fail if the exception is not raised. 

Let's run a pytest Pytest and see the output. To run the only tests from the test_exceptions.py file pytest run should look like this:

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If there is a need to have access to the actual exception info the pytest Pytest context manager optionally lets you add 'as your_text' like in the example below.  exception "exception_info" is an ExceptionInfo instance, which is a wrapper around the actual exception raised. The main attributes of interest are .type, .value and .traceback.

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Moreover, there is also a change that arguments provided to the test_select_item_from_list function have an improper type. To verify that we are going to check if the TypeError exception was raised. Let's add another test to test_selected_item_from_list():

def test_select_item_from_list():
    with pytest.raises(IndexError):
        select_item_from_list([1, 2, 3], 10)

    with pytest.raises(TypeError):
        select_item_from_list('list A', 'index')

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For ValueError example there is created new function called find_item_possition_in_list:

def find_item_position_in_list(lst, item):
    return lst.index(item)

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As expected there is no change to find a position of element '1' in an empty list. Let's run the test and check the output. 

The ValueError raised and testand test_find_item_position_in_list test passed.

The official documentation with listed available python built-in exceptions: https://docs.python.org/3/library/exceptions.html

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