Python Simple Function Tests Without a Testing Framework

This guide explains simple function tests without a testing framework through a focused Python example. You will learn the behavior to expect, why it matters in a real program, and how to recognize the common mistakes before applying it in your own project.

What You Will Learn

Even without unittest or pytest, a small function can be checked with a few carefully chosen assertions. Test a normal value, a boundary and a second representative input.

When and Why to Use It

The following example focuses on a practical use of Simple Function Tests Without a Testing Framework.

Step-by-Step Example

def is_even(number):
    return number % 2 == 0

assert is_even(4) is True
assert is_even(0) is True
assert is_even(7) is False
print("All checks passed")

Understanding the Example

Each assert checks that the function returns the expected boolean. The final message appears only if no assertion fails in a regular interpreter run.

Expected Output

All checks passed

Important Behavior and Edge Cases

Assertions can be disabled with the -O option and are not a substitute for validating untrusted user input.

Try It Yourself

Test a temperature conversion function using zero, a positive value and a negative value.

Common Beginner Mistakes

Assertions can be disabled with the -O option and are not a substitute for validating untrusted user input.
Confusing a returned value with printed output, or failing to verify a function’s behavior with different input values.
Skipping the practice step and assuming the example covers every input. Test at least one normal case and one edge case relevant to this topic.

Key Takeaways

Even without unittest or pytest, a small function can be checked with a few carefully chosen assertions.
Each assert checks that the function returns the expected boolean.
Apply the technique deliberately, checking its documented input requirements and failure behavior before integrating it into a larger project.