15.2.3 Test setUp and tearDown methods

The class unittest.TestCase provides two special methods, setUp and tearDown, which run before and after every call to a test method. This is needed when testing generators, which are exhausted after every test. We demonstrate this by testing a program that checks the line in a file in which a given string occurs for the first time:

class StringNotFoundException(Exception):
    pass

def find_string(file, string):
    for i,lines in enumerate(file.readlines()):
        if string in lines:
            return i
    raise StringNotFoundException(
          f'String {string} not found in File {file.name}.')

We assume that this code is saved in a file named find_in_file.py.

A test has to prepare a file and open it and remove it after the test as given in the following example:

import unittest
import os # used for, for example, deleting files

from find_in_file import find_string, StringNotFoundException...