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Getting Started with ETL Testing: A Shift in Mindset
When you start testing ETL (Extract, Transform, Load) systems, it becomes clear that it’s different from traditional software testing. While regular application testing often focuses on UI interaction and business logic, ETL testing is all about ensuring the data integrity, accuracy, and reliability of data as it flows from one system to another. It’s not just about “does it work,” but does the data make it through extraction, transformation, and loading processes correctly?
The Key Differences
1. Data Integrity
One of the biggest challenges in ETL testing is ensuring data integrity throughout the process. Unlike traditional testing where the focus is usually on user interaction, ETL testing requires you to compare source data with the target data to ensure nothing is missing or modified unintentionally.
For example, suppose you’re testing an e-commerce platform’s sales data. The ETL process extracts data from the transactional database, transforms it, and loads it into a data warehouse. You must check that the sales records, order numbers, and product IDs are the same in both the source and target tables. A simple SQL query can be used to compare the data:
SELECT
source.order_id,
source.product_id,
source.sale_amount…
