hypothesis-testing

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# Hypothesis Property-Based Testing

Hypothesis is a powerful property-based testing library that automatically generates test cases to find edge cases and validate properties of your code.

## Core Concept

**Traditional example-based testing:**
```python
def test_addition():
    assert add(2, 3) == 5
    assert add(0, 0) == 0
    assert add(-1, 1) == 0
```

**Property-based testing with Hypothesis:**
```python
from hypothesis import given
import hypothesis.strategies as st

@given(st.integers(), st.integers())
def test_addition_commutative(a, b):
    """Addition is commutative for ALL integers."""
    assert add(a, b) == add(b, a)
```

Hypothesis generates hundreds of test cases automatically, including edge cases you might not think of.

## Installation

```bash
# Install hypothesis with pytest integration
uv add --dev hypothesis pytest

# Optional plugins
uv add --dev hypothesis[numpy]      # NumPy strategies
uv add --dev hypothesis[pandas]     # Pandas strategies
uv add --dev hypothesis[django]     # Django model strategies
```

## Configuration

### pyproject.toml Configuration

```toml
[tool.pytest.ini_options]
# Hypothesis settings
addopts = [
    "--hypothesis-show-statistics",  # Show test statistics
    "--hypothesis-seed=0",            # Reproducible tests (optional)
]

[tool.hypothesis]
# Maximum number of examples to generate
max_examples = 200  # Default: 100, CI: 200+

# Deadline for each test case (milliseconds)
deadline = 1000  # Default: 200ms, None to disable

# Verbosity level (quiet, normal, verbose, debug)
verbosity = "normal"

# Fail fast on first error
derandomize = false  # Set to true for deterministic tests

# Database for example storage
database = ".hypothesis/examples"  # Store found failures

# Profile-specific settings
[tool.hypothesis.profiles.dev]
max_examples = 50
deadline = 1000
verbosity = "normal"

[tool.hypothesis.profiles.ci]
max_examples = 500
deadline = 5000
verbosity = "verbose"

[tool.hypothesis.profiles.debug]
max_examples = 10
deadline = null
verbosity = "debug"
```

### Activate Profile

```python
# tests/conftest.py
from hypothesis import settings, Verbosity

# Set default profile based on environment
import os
if os.getenv("CI"):
    settings.load_profile("ci")
else:
    settings.load_profile("dev")

# Or configure programmatically
settings.register_profile("custom", max_examples=100, deadline=500)
settings.load_profile("custom")
```

## Basic Usage

### Simple Property Tests

```python
from hypothesis import given, example
import hypothesis.strategies as st

# Test numeric properties
@given(st.integers())
def test_absolute_value_non_negative(x):
    """abs(x) is always non-negative."""
    assert abs(x) >= 0

@given(st.integers(), st.integers())
def test_addition_associative(a, b, c):
    """Addition is associative: (a + b) + c == a + (b + c)."""

From foryourhealth111-pixel/Vibe-Skills, Apache-2.0.

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