ETL Testing Interview Questions| Testing Interview Questions

Summary

In this mock interview, the candidate discusses their four years of experience as an ATL tester, working with tools like Oracle and Jira. They explain concepts such as ETL processes, data transformations, and their expertise in tools like Informatica. The interview covers technical topics such as active vs. passive transformations, lookup functions, partitioning, and testing strategies. The candidate also shares challenges faced in ETL testing, such as data loss and bulk data validation, while emphasizing the importance of continuous learning and staying updated with new tools like Linux. The session ends with advice on enhancing skills in test automation and programming.

Takeaways

• 😀 The candidate has 4 years of experience working with ETL testing, using tools like Oracle and Jira.
• 😀 The candidate is familiar with Informatica and its components, including repository, designer, monitor, and manager.
• 😀 A key difference between connected and unconnected lookups is that connected lookups directly receive input data, whereas unconnected lookups do not.
• 😀 Active transformations alter the number of rows in the data, while passive transformations do not.
• 😀 The candidate mentioned potential issues like wrong transformations, data loss, or data population errors during ETL testing.
• 😀 Workflow Monitor helps track errors and success/fail status, especially via session logs, which help identify exact errors in transformations.
• 😀 Partitioning in ETL testing improves performance by dividing large datasets into smaller parts for parallel processing.
• 😀 In a star schema, the fact table is surrounded by dimension tables. The fact table holds numerical data, while dimension tables contain descriptive data.
• 😀 The candidate follows Agile methodology for ETL testing, where requirements are analyzed, test cases are written, and execution follows after approval.
• 😀 The candidate emphasizes the importance of keeping updated on new tools and technologies through sources like social media, YouTube, and personal learning.

Q & A

What is the main purpose of using Informatica ETL tool?

Informatica is used for Extract, Transform, and Load (ETL) processes. It helps in applying business logic, cleansing data, and moving data from source to target systems efficiently.

Can you explain the difference between connected and unconnected lookup in ETL testing?

In a connected lookup, data is directly received as input values from the transformation pipeline, whereas in an unconnected lookup, it receives values from functions or results, not directly from the pipeline. Additionally, connected lookup supports both static and dynamic cache, while unconnected lookup only supports static cache.

How does partitioning improve ETL process performance?

Partitioning divides large datasets into smaller parts, which can be processed in parallel. This reduces the processing time and improves overall system performance and efficiency.

What is the significance of the fact table and dimension table in a star schema?

In a star schema, the fact table contains quantitative data like numerical values or business measures, whereas dimension tables contain descriptive data, such as names or categories, which provide context to the fact data.

What challenges do ETL testers face when dealing with heterogeneous data sources?

ETL testers face challenges in working with various data platforms, ensuring data integrity across different formats, and handling data loss, especially when large volumes of data are transferred from source to target.

What are some common ETL testing bugs that testers encounter?

Common ETL testing bugs include count mismatches, null values populated in target systems, junk data containing special characters, and extra data loaded into the target system.

Can you explain the difference between active and passive transformations in ETL?

An active transformation changes the number of rows during data processing, whereas a passive transformation does not alter the number of rows, keeping the data unchanged in terms of its row count.

How do you handle missing test cases or missed scenarios during a demo presentation to the client?

If a scenario is missed, the team can request more time from the client for retesting or fixing the issue. The missed scenario can be included in the test case repository and tested in the next sprint.

What strategies do you use to stay updated on new ETL tools and technologies?

To stay updated, I follow various online learning platforms, social media, and YouTube channels. I also learn directly from my work and engage with community resources.

What are the key steps involved in the ETL testing process?

The key steps in ETL testing include requirement analysis, test case creation, test estimation, execution, bug identification, and reporting. This process is done in iterative cycles, especially in agile methodologies.