Property-Based Testing
Instead of writing individual test cases with fixed inputs, you define properties (invariants) that should always be true for any valid input.
How it Works
- Define a strategy for generating random data (e.g., "any list of integers").
- Define a property (e.g., "sorting a list doesn't change its length").
- The framework generates hundreds of inputs to find a counter-example.
- If it finds one, it shrinks the input to the simplest possible case that fails.
Tools
- Python: Hypothesis
- JavaScript: fast-check
- Rust: proptest
Example (Python with Hypothesis)
from hypothesis import given, strategies as st
def add(a, b):
return a + b
@given(st.integers(), st.integers())
def test_add_commutative(a, b):
assert add(a, b) == add(b, a)
When to Use
- Mathematical functions.
- Encoders/Decoders.
- Data transformation pipelines.
- Sorting or searching algorithms.
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