Property-Based Testing with jqwik: A Practical Guide

A guide how to write property-based tests in Java: theory and practice

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Introduction

As software grows more complex, traditional example-based testing often fails. It can’t find edge cases and unexpected behaviors. Property-based testing (PBT) is a powerful alternative. It generates test cases based on properties that your code should meet without any manual input. This article will explore property-based testing using jqwik. It’s a modern property-based testing library for Java.

What is property — based testing?

Property-based testing is a method. Instead of writing specific test cases, you define properties. Your code must meet them in all cases. The testing framework then generates many test cases to verify these properties.

Difference between traditional unit testing and property — based testing

For example, instead of writing

@Test
void testReverse() {
    assertEquals("cba", StringUtils.reverse("abc"));
}

You would define a property:

@Property
void reverseStringTwiceShouldGiveOriginalString(@ForAll…