Step-by-Step Guide to Writing ETL Test Cases

Step-by-Step Guide to Writing ETL Test Cases

1. Understand the ETL Process and Requirements

Review ETL specifications, mappings, and business logic.


Understand source systems, data flow, transformation rules, and target systems.


Clarify any ambiguities with stakeholders or developers.


2. Identify Test Scenarios

ETL test cases are usually categorized into:


Data Extraction Testing


Data Transformation Testing


Data Loading Testing


Data Quality Testing


Performance Testing


For each, list scenarios such as:


Source to staging extraction


Transformation rules verification


Target data accuracy and completeness


Handling null values, duplicates, and error logs


Incremental load validation


3. Define Test Case Template

Common fields to include:


Field Description

Test Case ID Unique identifier

Test Scenario The scenario to test

Pre-Conditions Data/environment setup

Test Steps Step-by-step instructions

Test Data Sample data used

Expected Result What is expected after execution

Actual Result Actual outcome after execution

Status Pass/Fail

Comments/Notes Additional observations


4. Write Test Cases for Data Extraction

Verify the full extraction of data from source systems.


Confirm data format, field types, and volume match the source.


Test for missing or incomplete data extraction.


Example:


Test Case ID Scenario Pre-Condition Test Steps Test Data Expected Result

TC_ETL_001 Verify data extraction from DB1 Data present in DB1 1. Run extraction process 2. Query extracted data Source table rows Extracted rows count = source rows count


5. Write Test Cases for Data Transformation

Validate all transformation rules (calculations, concatenations, filters).


Check data type conversions and format changes.


Verify business logic application.


Example:


Test Case ID Scenario Pre-Condition Test Steps Test Data Expected Result

TC_ETL_002 Validate currency conversion Source currency = USD 1. Run transformation 2. Check target currency $100 USD in source data Target currency converted correctly to EUR at rate


6. Write Test Cases for Data Loading

Confirm that transformed data is loaded into the target system accurately.


Test for data completeness and correctness.


Check for duplicate or missing records.


Example:


Test Case ID Scenario Pre-Condition Test Steps Test Data Expected Result

TC_ETL_003 Verify data loading in target DB Data transformed correctly 1. Load data 2. Query target DB Transformed data Number of rows in target = Number of transformed rows


7. Write Test Cases for Data Quality

Validate null, default values, and data integrity.


Verify duplicate data handling.


Check for data consistency between source and target.


Example:


Test Case ID Scenario Pre-Condition Test Steps Test Data Expected Result

TC_ETL_004 Check for duplicates Data with duplicates 1. Run ETL 2. Query for duplicates Duplicate records No duplicates found in target table


8. Write Test Cases for Performance and Incremental Loads

Verify ETL job runtime within expected time.


Test incremental or delta loads for new or updated data only.


Check resource usage and scalability.


Example:


Test Case ID Scenario Pre-Condition Test Steps Test Data Expected Result

TC_ETL_005 Validate incremental load Initial full load done 1. Load incremental data 2. Verify only new records loaded Incremental dataset Only new or updated rows present in target


9. Review and Validate Test Cases

Peer review for completeness and accuracy.


Align test cases with business rules.


Update based on feedback.


10. Execute and Document Test Cases

Execute test cases in the test environment.


Document actual results and compare with expected results.


Log defects if any discrepancies are found.


Bonus Tips:

Automate repetitive ETL tests using scripts or ETL testing tools.


Maintain traceability between requirements, test cases, and defects.


Keep test data representative of real-world scenarios.

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