What is ETL testing?
ETL testing verifies that data extracted, transformed and loaded between systems arrives complete and correct.
ETL and ELT pipelines move data from operational systems into warehouses and analytics tools. ETL testing checks completeness, transformation logic, data quality and freshness at each stage.
Because pipeline failures are often silent, wrong numbers can reach dashboards and models without any error being raised.
Example
An ETL test compares daily order counts in the source database with the warehouse and flags that one region’s orders were dropped by a new filter.
Best practices
- Reconcile counts and sums from source to target
- Test transformation rules with known inputs
- Check nulls, duplicates and ranges
- Alert on late or partial loads
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