05 Checkpoint: Testing Functions

Purpose

Improve your ability to verify the correctness of functions by writing a test function and running it with pytest.

Assignment

Write a test function that tests a previously written function. Then use pytest to run test functions.

Helpful Documentation

pip is a standard Python module that you can use to download and install third-party modules. During the checkpoint of this lesson, you will use pip to download and install pytest, so that you can use pytest in your test code.
This video about the pip module (16 minutes) shows a BYU-Idaho faculty member using pip to install other Python modules.
The prepare content for this lesson explains how to use pytest, assert, and approx to automatically verify that functions are correct. It also contains an example test function and links to additional documentation about pytest.
This video about test functions (20 minutes) shows a BYU-Idaho faculty member writing two test functions and using pytest to run them.

Steps

Do the following:

Open a new terminal frame in VS Code by doing the following:
1. Open VS Code
2. On the menu bar for VS Code, click "Terminal"
3. On the menu, click "New Terminal"
This will open a terminal frame at the bottom of the VS Code window. A terminal is a window or frame where a user can type and execute computer commands.
Copy and paste the following command into the terminal frame and execute the command by pressing the Enter key. This command will upgrade pip and several other parts of the Python installation modules so that pip will work correctly.
- Mac OS users:
```
python3 -m pip install --user --upgrade pip setuptools wheel
```
- Windows users:
```
python -m pip install --user --upgrade pip setuptools wheel
```
  - If your computer is running the Windows operating system, and the above command doesn’t work on your computer, try the py command instead of the python command like this:
```
py -m pip install --user --upgrade pip setuptools wheel
```
Install the pytest module by copying, pasting, and executing the following command in the terminal frame.
- Mac OS users:
```
python3 -m pip install --user pytest
```
- Windows users:
```
python -m pip install --user pytest
```
  - If your computer is running the Windows operating system, and the above command doesn’t work on your computer, try the py command instead of the python command like this:
```
py -m pip install --user pytest
```
Download these two Python files: words.py and test_words.py and save them in the same folder.
Open the downloaded words.py file in VS Code. Notice the words.py file contains two small functions named prefix and suffix. Notice also that each function has a documentation string (a triple quoted string immediately below a function header) that describes what the function does. Read the documentation strings for both functions.
Open the downloaded test_words.py file in VS Code. In test_words.py examine the test_prefix function. Notice that it takes no parameters and contains nine assert statements. Each assert statement calls the prefix function and then compares the value returned from the prefix function to the expected value.

In test_words.py write a function named test_suffix that is similar to the test_prefix function. The test_suffix function should take no parameters and contain nine assert statements that call the suffix function with these parameters:

Arguments		Expected Return Value
s1	s2	Expected Return Value
""	""	""
""	"correct"	""
"clear"	""	""
"angelic"	"awesome"	""
"found"	"profound"	"found"
"ditch"	"itch"	"itch"
"happy"	"funny"	"y"
"tired"	"fatigued"	"ed"
"swimming"	"FLYING"	"ing"

Save your test_words.py file and run it by clicking the green run icon in VS Code.

Testing Procedure

Verify that your test program works correctly by following each step in this procedure:

Run your test program and ensure that your test program’s output is similar to the sample run output below.

> python test_words.py
=================== test session starts ====================
platform win32--Python 3.8.6, pytest-6.1.2, py-1.9.0, pluggy
rootdir: C:\Users\cse111\lesson05
collected 2 items

test_words.py::test_prefix PASSED                     [ 50%]
test_words.py::test_suffix PASSED                     [100%]

==================== 2 passed in 0.09s =====================

Sample Solution

When your program is finished, view the sample solution for this assignment to compare your solution to that one. Before looking at the sample solution, you should work to complete this checkpoint program. However, if you have worked on it for at least an hour and are still having problems, feel free to use the sample solution to help you finish your program.

Call Graph

The following call graph shows the function calls and returns in the sample solution for this assignment. From this call graph we see that the computer starts executing the sample test functions by calling the pytest.main function. While executing the pytest.main function, the computer calls the test_prefix function. While executing the test_prefix function, the computer calls the prefix function. Then while still executing the pytest.main function, the computer calls the test_suffix function. While executing the test_suffix function, the computer calls the suffix function.

Ponder

During this assignment, you downloaded a Python file that contains two program functions named prefix and suffix. You wrote a test function named test_suffix that is similar to the test_prefix function that was given to you. You used pytest to run both test functions and examined the output of pytest to verify that the test functions passed. Because the test functions called prefix and suffix with many different arguments and verified (using assert) that the values returned from prefix and suffix were correct, we can assume that the prefix and suffix functions work correctly. Do you think writing and running test functions will help you write better programs?

Submission

When complete, report your progress in the associated I‑Learn quiz.