“Testing 1, 2, 3” Exercise

To setup this exercise, bring up an existing repository, or create a new repository called “testing-123”. Navigate there from the command line, and open the repository using your text editor.

Inside the repository, create subdirectories called “app” and “test”, respectively.

In the “app” subdirectory, create a new file called “utils.py”, and place inside the following contents:

# this is the "app/utils.py" file:

def enlarge(i):
    return i * 100


if __name__ == "__main__":

    my_number = float(input("Please input a number: "))
    print(my_number)

    result = enlarge(my_number)
    print(result)

Observe, we can run this file from the command-line:

python -m app.utils

In the “test” subdirectory, create a new file called “utils_test.py”, and place inside the following contents:

# this is the "test/utils_test.py" file...

from app.utils import enlarge

def test_enlarge():
    result = enlarge(3)
    assert result == 300

Observe, the test file imports the function we want to test from where it has been defined, contains a test function which directly invokes the function we want to test, and describes expectations for what it means for that function to be working properly.

We will use the pytest package to find and run these tests. There are some rules about how to name your tests in order for pytest to be able to successfully find and run them:

• The test directory name must be “test” singular or “tests” plural.
• The test file name must begin with “test_” or end with “_test.py”.
• The test function name must begin with “test_”.

We run the tests from the command-line using the pytest package (which needs to be installed first):

pytest

If you run into an error “ModuleNotFoundError: No module named ‘app’”, you need to add some configuration files to help pytest find and import code from the “app” directory:

1. Add a special file called the “__init__.py” to the “app” directory. This is a Python convention that enables code in this module to be found and imported.
2. Add another special file called “conftest.py” to either the repository’s root directory, or into the “test” directory. This helps orient pytest to the structure of your repository.

Even if these files are blank, their presence will help us avoid the errors we were seeing earlier.

Once you have finished configuring the “app/__init__.py” and “conftest.py” files, run the tests again, and they should pass:

pytest #> 1 passed in 0.01 seconds

Nice job! You’re testing like a pro!