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ETL Testing Unveiled: Your Ultimate Guide to Seamless Data Integration

December 18, 2023
An IT professional working on a digital tablet with extract transform load(ETL) icon on virtual screen illustrate ETL testing.

ETL, short for Extract, Transform, and Load, is the mantra that drives the world of data. Without ETL, valuable data would lie scattered across millions of digital sources and remain invaluable for further use. ETL testing consolidates the scattered data into a single repository, repurposes it for analysis, and facilitates decision-making processes.

If you are into ETL testing, this article is for you, since it explores beyond ETL testing introduction. Let’s go!

What is ETL Testing?

ETL testing is an approach to integrating data from diverse sources (Extract), transforming it into various styles and formats (Transform), and loading the newly transformed data into databases or warehouses for further use (Load).

When processing and migrating data to a new location, it is crucial to ensure that your data is of the highest quality. Here’s where ETL testing steps in. This process evaluates if your data:

  • Is accurate, complete, and reliable.
  • Represents information from various pipelines.
  • Is correctly loaded into your new data warehouse or system.

ETL testing doesn’t end here. Data integration from disparate sources requires careful attention to detail. Despite best efforts, collated data is prone to errors that compromise data quality and accuracy. Here again, ETL testing helps identify and rectify mistakes such as:

  • Contaminated data that does not comply with data mapping rules.
  • Non-standard and inconsistent formats between the source and target database.
  • Bugs when the system cannot support large data volumes or multiple users.
  • Incorrect values in the source database result in loss of data at a destination.
  • Bugs in input or output when invalid values are accepted, and valid ones are rejected.
  • Data loss and duplication of records.

When Is It Necessary to Perform ETL Testing?

During ETL testing, data is verified at several critical junctures to ensure accuracy and consistency. These checks allow data professionals to identify and correct issues early on and minimize the risk of costly errors.

Throughout the entire ETL process, the ETL tester is responsible for ensuring accurate data extraction, transfer, and loading into the new system. They are also responsible for conducting ETL testing after:

  • The first data loading into a new data warehouse
  • Adding a new data source to an existing data source
  • A new data migration

ETL testing is also conducted during data migration and if there are concerns regarding the data quality or ETL process performance. Effective ETL testing detects issues with source data before it's loaded into the repository and finds inconsistencies in business rules guiding data integration.

To understand ETL better, let’s discuss the stages of this crucial process in detail.

8 Stages of ETL Testing: From Start to End

Stage 1: Business requirement identification

This initial stage involves designing the data model, defining the business flow, and evaluating the client’s expectations. These aspects lay the fundamentals that define the project scope, document it, and ensure that testers fully understand it.

Stage 2: Data source validation

In this stage, testers:

  • Perform data count checks
  • Verify that the table and column data types meet the data model specifics.
  • Ensure that check keys are in place
  • Remove duplicate data to ensure accuracy in aggregate reports

Stage 3: ETL map designing

Testers create ETL mapping for various scenarios, write SQL scripts, and list the transformational rules. Each ETL mapping comprises:

  • Test action plans and solutions to address multiple challenges
  • Data required to fulfil client’s expectations

Generally, this mapping is pre-approved by the head of Quality Analysis.

Stage 4: Data extraction from sources

In this crucial stage, testers perform ETL tests according to the business requirements, identify bugs and defects, fix the issues, and draft and close reports before moving on to the next stage.

Stage 5: Transformation logic application

Testers execute data transformation to match the schema of the target data warehouse. They also check the data threshold and alignment to validate data flow. This ensures that each column and table matches the mapping document's data type.

Stage 6: Data loading into the warehouse

Before and after migrating data to a warehouse, testers check the record count to confirm that all invalid data is removed and default values are accepted.

Stage 7: Summary report preparation

The Quality Analysis team prepares a r=summary report at the end of the ETL process. This report comprises:

  • The findings of the tests
  • Documented bugs and errors
  • The outcome of the ETL test process

Stage 8: Final closing and reporting

Testers file and submit the ETL test closure report in this last and final stage.
The overall objective of ETL testing is to ensure error-free data transfer from the source to a target database or warehouse. The process itself is designed to address any challenges during the cycle. At different stages, various types of tests are conducted. Let’s analyze them in the following segment.

Also Read: 10 Must-Have AWS Skills to Supercharge Your Career

10 Types of ETL Testing You Should Know About

1. Production Validation Testing

Error-free data is crucial for ETL testing since it guarantees accurate analysis reports. Production validation testing checks and validates the transferred data in the production system and compares it with the source data.

2. Source to Target Data Testing

It verifies that data transferred to the target system has no loss or truncation and adheres to expected values after transformation.

3. Source-to-target Count Testing

This test:

  • Verifies if the source system data count matches the data loaded in the target system.
  • Estimates the out even if it is not accurate or reliable.

However, the test doesn’t involve minute details like the value, order, and type of the data loaded.

4. Metadata Testing

Metadata is the type of data detailing the structure and data relationship. This test involves checks the following:

  • Data type, index, and length
  • Data constraints

It also ensures that it adheres to the data and is used appropriately in the ETL process.

5. Completeness Testing

As the name implies, this test ensures that all the disparately sourced data is loaded into the target without duplication or loss.

6. Transformation Testing

This test checks if data has been consistently transformed according to multiple rules. It ensures that the data has been changed the same way every single time.

7. Accuracy Testing

This test verifies the transferred data for accuracy, although the schema and data formats are different after transformation.

8. Performance Testing

The objective of this test is to:

  • Ensure that the loaded data is within the prescribed time frame
  • Check if the system can handle the current user traffic
  • Check if it can handle the increase in the number of users accessing the data

9. Data Integration Testing

This testing involves:

  • Verification to ascertain if data from disparate sources are migrated as expected.
  • Checking of threshold values.
  • Integration of data into the warehouse post-transformation and loading.

10. Report Testing

This test checks the accuracy of the reported data. Testers rely on several calculations to assess the accuracy and verify the data layout and functionality as per the model.

To Summarise

When it comes to data, ETL plays a significant role in ensuring its accuracy and reliability, which are crucial in an organization’s data-based decision-making process. Our blog also highlights the importance of ETL testers and how their expertise makes a difference in ETL testing.

There will always be a constant need for ETL testers as long as data continues to exist. Join Aimore, the leading Software Training Institute in Chennai, and enrol in our top-notch ETL testing courses in Chennai now. Grab the opportunity and make the most of it to lay the foundation for a bright career. Contact us for further details.

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