ETL TESTING CHEAT SHEET | QA SDET | INTERVIEW QUESTIONS
ETL (Extract, Transform, Load) testing ensures that data is correctly extracted from source systems, transformed according to business rules, and loaded accurately into target systems (data warehouses or databases).
1. ETL Testing Phases
The process involves several structured phases including requirement gathering, data source validation, reviewing ETL mappings, test planning, test case development, execution, defect tracking, and final sign-off.
2. Key ETL Test Scenarios
Critical test scenarios include:
Count checks between source and target.
Data type and null validation.
Transformation logic verification.
Duplicate detection.
Data consistency with lookups and joins.
Date format and incremental load validation.
3. Useful SQL Queries
ETL testers often use SQL to:
Count records,
Identify null or duplicate values,
Check data types,
Validate transformation rules using CASE statements, and
Compare source vs. target data.
4. Best Practices
To ensure thorough validation:
Review mappings carefully,
Use hash/checksum functions for large datasets,
Document all transformations and assumptions,
Leverage automation tools like Informatica, Talend, or Airflow,
Maintain clear traceability of test data.