testing-patterns

# Testing Patterns

Pytest templates for comprehensive ETL pipeline testing.

## Unit Tests - Transform Functions

```python
# tests/test_transforms.py
import pytest
import pandas as pd
from pipeline.transforms import clean_email, calculate_total, categorize_customer

class TestCleanEmail:
    def test_lowercase(self):
        assert clean_email("John@Example.COM") == "john@example.com"

    def test_strip_whitespace(self):
        assert clean_email("  john@example.com  ") == "john@example.com"

    def test_invalid_returns_none(self):
        assert clean_email("not-an-email") is None

    def test_null_input(self):
        assert clean_email(None) is None


class TestCalculateTotal:
    @pytest.fixture
    def order_items(self):
        return pd.DataFrame({
            'order_id': [1, 1, 2],
            'quantity': [2, 3, 1],
            'unit_price': [10.0, 5.0, 100.0]
        })

    def test_sums_correctly(self, order_items):
        result = calculate_total(order_items)
        assert result.loc[result['order_id'] == 1, 'total'].values[0] == 35.0

    def test_handles_empty(self):
        empty = pd.DataFrame(columns=['order_id', 'quantity', 'unit_price'])
        result = calculate_total(empty)
        assert len(result) == 0


class TestCategorizeCustomer:
    @pytest.mark.parametrize("total_spent,expected", [
        (0, 'bronze'),
        (99, 'bronze'),
        (100, 'silver'),
        (999, 'silver'),
        (1000, 'gold'),
        (9999, 'gold'),
        (10000, 'platinum'),
    ])
    def test_tiers(self, total_spent, expected):
        assert categorize_customer(total_spent) == expected
```

## Integration Tests - Full Pipeline

```python
# tests/test_pipeline.py
import pytest
from pipeline import OrdersPipeline
from tests.fixtures import generate_orders_fixture

class TestOrdersPipeline:
    @pytest.fixture
    def pipeline(self, tmp_path):
        return OrdersPipeline(
            source_path=tmp_path / "source",
            target_path=tmp_path