Data Quality Frameworks

2. Testing Pyramid for Data

          /\
         /  \     Integration Tests (cross-table)
        /────\
       /      \   Unit Tests (single column)
      /────────\
     /          \ Schema Tests (structure)
    /────────────\

Quick Start

Great Expectations Setup

# Install
pip install great_expectations

# Initialize project
great_expectations init

# Create datasource
great_expectations datasource new

# great_expectations/checkpoints/daily_validation.yml
import great_expectations as gx

# Create context
context = gx.get_context()

# Create expectation suite
suite = context.add_expectation_suite("orders_suite")

# Add expectations
suite.add_expectation(
    gx.expectations.ExpectColumnValuesToNotBeNull(column="order_id")
)
suite.add_expectation(
    gx.expectations.ExpectColumnValuesToBeUnique(column="order_id")
)

# Validate
results = context.run_checkpoint(checkpoint_name="daily_orders")

Patterns

Pattern 1: Great Expectations Suite

# expectations/orders_suite.py
import great_expectations as gx
from great_expectations.core import ExpectationSuite
from great_expectations.core.expectation_configuration import ExpectationConfiguration

def build_orders_suite() -> ExpectationSuite:
    """Build comprehensive orders expectation suite"""

    suite = ExpectationSuite(expectation_suite_name="orders_suite")

    # Schema expectations
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_table_columns_to_match_set",
        kwargs={
            "column_set": ["order_id", "customer_id", "amount", "status", "created_at"],
            "exact_match": False  # Allow additional columns
        }
    ))

    # Primary key
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_not_be_null",
        kwargs={"column": "order_id"}
    ))
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_be_unique",
        kwargs={"column": "order_id"}
    ))

    # Foreign key
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_not_be_null",
        kwargs={"column": "customer_id"}
    ))

    # Categorical values
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_be_in_set",
        kwargs={
            "column": "status",
            "value_set": ["pending", "processing", "shipped", "delivered", "cancelled"]
        }
    ))

    # Numeric ranges
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_be_between",
        kwargs={
            "column": "amount",
            "min_value": 0,
            "max_value": 100000,
            "strict_min": True  # amount > 0
        }
    ))

    # Date validity
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_values_to_be_dateutil_parseable",
        kwargs={"column": "created_at"}
    ))

    # Freshness - data should be recent
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_max_to_be_between",
        kwargs={
            "column": "created_at",
            "min_value": {"$PARAMETER": "now - timedelta(days=1)"},
            "max_value": {"$PARAMETER": "now"}
        }
    ))

    # Row count sanity
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_table_row_count_to_be_between",
        kwargs={
            "min_value": 1000,  # Expect at least 1000 rows
            "max_value": 10000000
        }
    ))

    # Statistical expectations
    suite.add_expectation(ExpectationConfiguration(
        expectation_type="expect_column_mean_to_be_between",
        kwargs={
            "column": "amount",
            "min_value": 50,
            "max_value": 500
        }
    ))

    return suite

Pattern 2: Great Expectations Checkpoint

# great_expectations/checkpoints/orders_checkpoint.yml