Generate Unit Tests Free — Paste Your Code, Get Tests
Paste a function and get complete unit test code in seconds. Works with Python pytest, Python unittest, and JavaScript Jest — free, unlimited, no signup.
Free forever · no signup · no credit card · unlimited
import os
# Folder to clean up — change this to your path
FOLDER = "./photos"
for i, name in enumerate(sorted(os.listdir(FOLDER)), start=1):
src = os.path.join(FOLDER, name)
if not os.path.isfile(src):
continue
ext = os.path.splitext(name)[1].lower()
dst = os.path.join(FOLDER, f"photo_{i:03d}{ext}")
os.rename(src, dst)
print(f"{name} -> {os.path.basename(dst)}")This script renames every file in a folder to photo_001, photo_002, and so on, keeping each file’s extension. Set FOLDER to your folder, then run python rename.py from a terminal.
This free unit test generator writes test cases for your functions automatically. Give it a function and it produces tests covering normal behavior, edge cases, and error conditions. Whether you are learning testing for the first time or speeding up your workflow, get working test code in seconds — no signup required.
How to Generate Unit Tests
Paste your function
Copy the function you want to test and paste it into the input. Include the function signature, parameters, and any relevant context about what it should do.
Specify your test framework (optional)
Mention pytest, unittest, or Jest if you have a preference. If you do not specify, the generator chooses based on the language of your code.
Click Generate
The AI reads your function and generates test cases covering normal inputs, edge cases (empty inputs, zero, None), and error conditions (invalid types, out-of-range values).
Run the tests
Copy the test file into your project and run it. For Python: pytest test_file.py or python -m unittest test_file.py. For JavaScript/Jest: npx jest test_file.test.js.
Add your own cases
Use the generated tests as a foundation. Add your own test cases for business-specific logic or edge cases only you know about.
About This Unit Test Generator
Unit tests are small, automated checks that verify a single function or module works as expected. They are one of the most effective practices for catching bugs early, preventing regressions when code changes, and documenting how a function is supposed to behave. Despite their value, writing tests is often tedious — this generator takes the boilerplate off your hands so you can focus on your actual code.
A unit test typically follows the Arrange-Act-Assert pattern. Arrange: set up the inputs. Act: call the function. Assert: check that the output or behavior matches the expectation. For example, to test a function called add(a, b): arrange with a=2 and b=3, act by calling add(2, 3), and assert that the result equals 5.
In Python, the two main testing frameworks are pytest and unittest. pytest is the more popular modern choice — it requires minimal boilerplate, uses plain assert statements, and has a rich plugin ecosystem. To run pytest, install it with pip install pytest, save your test file with a name starting with test_, and run pytest in your project folder. unittest is part of the Python standard library and needs no installation. Tests are written as classes inheriting from unittest.TestCase with methods named test_*. Run with python -m unittest or python -m pytest.
In JavaScript, Jest is the dominant testing framework for both Node.js and React projects. Install it with npm install --save-dev jest. Write test files with .test.js or .spec.js extensions. Run tests with npx jest. Jest uses describe() blocks to group related tests and it() or test() functions for individual cases. The expect() function provides assertions: expect(add(2, 3)).toBe(5).
Good unit tests cover multiple scenarios. Happy path tests verify the function works with normal, expected inputs. Edge case tests check boundaries — empty arrays, zero values, the minimum and maximum allowed values, single-element lists. Error case tests verify that the function throws the right error when given invalid inputs. The generated tests cover all three categories automatically.
Test coverage is a metric that measures what percentage of your code is executed by your tests. High coverage (80–100%) means most code paths are tested. In Python, run pytest --cov=your_module to see coverage. In JavaScript, run jest --coverage. Coverage is a useful guide but not a guarantee — a test that calls every line without meaningful assertions does not catch real bugs.
Even if you are new to programming, starting with unit tests is one of the best habits to build. Tests give you confidence when refactoring, serve as documentation for how functions should behave, and catch mistakes before they reach users.
Frequently asked questions
Is this unit test generator free?
Yes, completely free. No account, no signup, unlimited generations.
Which testing frameworks does it support?
Python pytest, Python unittest, and JavaScript Jest. Specify your preference or the AI will choose based on your code's language.
Do I need to know how to write tests to use this?
Not at all. Paste your function and get complete test code. Reading the generated tests is also a good way to learn test-writing patterns.
Will the generated tests catch all bugs?
The generator creates a strong foundation of tests for common scenarios and edge cases. However, tests for business-specific logic or unusual inputs may need to be added manually. No test suite guarantees zero bugs.
How do I run the tests?
For Python pytest: install with pip install pytest, then run pytest in your terminal. For Python unittest: run python -m unittest test_file. For Jest: install with npm install --save-dev jest, then run npx jest.
Can it generate tests for a whole file or class, not just one function?
Yes. Paste your entire class or module and ask for tests covering all methods. The generator handles classes with multiple methods and generates grouped test cases.