> ## Documentation Index
> Fetch the complete documentation index at: https://mcp-server-langgraph.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# 16. Property-Based Testing with Hypothesis

> Architecture Decision Record: 16. Property-Based Testing with Hypothesis

# 16. Property-Based Testing with Hypothesis

Date: 2025-10-13

## Status

Accepted

## Category

Testing & Quality

## Context

Traditional unit tests check specific examples:

```python theme={null}
assert calculate_discount(100, 0.1) == 90
```

Edge cases often missed:

* Negative numbers
* Zero values
* Very large numbers
* Unicode in strings

## Decision

Use **Hypothesis for property-based testing** to discover edge cases automatically.

### Example

```python theme={null}
from hypothesis import given
from hypothesis.strategies import integers, floats

@given(price=floats(min_value=0), discount=floats(min_value=0, max_value=1))
def test_discount_properties(price, discount):
    result = calculate_discount(price, discount)
    assert result >= 0  # Never negative
    assert result <= price  # Never more than original
```

Hypothesis generates 100+ test cases including edge cases.

## Consequences

### Positive

* **Edge Case Discovery**: Finds bugs unit tests miss
* **Higher Confidence**: Tests properties, not examples
* **Less Test Code**: One property test replaces many examples
* **Regression Prevention**: Generated cases saved on failure

### Negative

* **Slower Tests**: 100 cases per test vs 1
* **Learning Curve**: Property thinking vs example thinking
* **Flaky Tests**: Random generation can cause intermittent failures

## Usage

27+ property tests covering:

* LLM factory fallback logic
* Authentication providers
* Session management
* Role mapping

## References

* Tests: `tests/property/`
* Dependency: `pyproject.toml:66` - `hypothesis>=6.100.0`