testing-python

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• SKILL.md

SKILL.md (first lines)

# Writing Effective Python Tests

## Core Principles

Every test should be **atomic**, **self-contained**, and test **single functionality**. A test that tests multiple things is harder to debug and maintain.

## Test Structure

### Atomic unit tests

Each test should verify a single behavior. The test name should tell you what's broken when it fails. Multiple assertions are fine when they all verify the same behavior.

```python
# Good: Name tells you what's broken
def test_user_creation_sets_defaults():
    user = User(name="Alice")
    assert user.role == "member"
    assert user.id is not None
    assert user.created_at is not None

# Bad: If this fails, what behavior is broken?
def test_user():
    user = User(name="Alice")
    assert user.role == "member"
    user.promote()
    assert user.role == "admin"
    assert user.can_delete_others()
```

### Use parameterization for variations of the same concept

```python
import pytest

@pytest.mark.parametrize("input,expected", [
    ("hello", "HELLO"),
    ("World", "WORLD"),
    ("", ""),
    ("123", "123"),
])
def test_uppercase_conversion(input, expected):
    assert input.upper() == expected
```

### Use separate tests for different functionality

Don't parameterize unrelated behaviors. If the test logic differs, write separate tests.

## Project-Specific Rules

### No async markers needed

This project uses `asyncio_mode = "auto"` globally. Write async tests without decorators:

```python
# Correct
async def test_async_operation():
    result = await some_async_function()
    assert result == expected

# Wrong - don't add this
@pytest.mark.asyncio
async def test_async_operation():
    ...
```

### Imports at module level

Put ALL imports at the top of the file:

```python
# Correct
import pytest
from fastmcp import FastMCP
from fastmcp.client import Client

async def test_something():
    mcp = FastMCP("test")
    ...

# Wrong - no local imports
async def test_something():
    from fastmcp import FastMCP  # Don't do this
    ...
```

### Use in-memory transport for testing

Pass FastMCP servers directly to clients:

```python
from fastmcp import FastMCP
from fastmcp.client import Client

mcp = FastMCP("TestServer")

@mcp.tool
def greet(name: str) -> str:
    return f"Hello, {name}!"

async def test_greet_tool():
    async with Client(mcp) as client:
        result = await client.call_tool("greet", {"name": "World"})
        assert result[0].text == "Hello, World!"
```

Only use HTTP transport when explicitly testing network features.

### Inline snapshots for complex data

Use `inline-snapshot` for testing JSON schemas and complex structures:

```python
from inline_snapshot import snapshot

def test_schema_generation():
    schema = generate_schema(MyModel)
    assert schema == snapshot()  # Will auto-populate on first run
```

From benchflow-ai/skillsbench, Apache-2.0.

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