ETL Testing Interview Questions and Answers

List of Most Frequently Asked ETL Testing Tools Interview Questions And Answers to Help You Prepare For The Upcoming Interview:

Business information and the data are of key importance to any business and company. Many companies invest a lot of time and money in the process of analyzing and sorting out this vital information.

Analyzing and Integration of Data has gained a huge potential market and so to make this process organized and simple, ETL testing tools have been introduced by many software vendors.

There are many open-source ETL tools available in the market, where the vendors allow the users to directly download the free versions from their official website. All the basic functions will be available in this free version download but to upgrade to the next level, the company needs to subscribe to the vendors on payment.

ETL Testing

Each company has a different business structure and model, so they need to make a clear analysis before choosing the ETL tool for their business. With the help of these open source ETL tools, the business has the opportunity to try out the free software tools without any huge investments.

All the software giants have introduced their own BI tools.

Most used ETL tools are as enlisted below:

  • Talend Open Studio
  • Clover ETL
  • Elixir
  • Pentaho
  • Informatica
  • IBM – Cognos Data Manager
  • Oracle – Data Integrator
  • SAS – Data Integration Studio
  • AB Initio, SAP – Business Objects Data Integrator

When an ETL tool is selected, the next logical step would be testing using these tools. Here, the company will get to know if they are on the right path in the selection of the tool.

As these tools help in dealing with a huge amount of data and historic data, it is necessary to carry out the ETL testing. To keep a check on the accuracy of the data, ETL testing is very important.

There are two types of ETL testing available:

  • Application Testing
  • Data Eccentric Testing

ETL Testing Process:

Although there are many ETL tools, a simple testing process is commonly used in ETL testing. It is as important as the implementation of the ETL tool into your business.

Having a well-defined ETL testing strategy can make the testing process much easier. Hence, this process needs to be followed before you start the Data Integration processed with the selected ETL tool.

In this process, a group of experts comprising the programming and developing team will start writing SQL statements. The development team may customize according to the requirements.

ETL testing process includes:

  • Analyzing the requirement: Understanding the business structure and their particular requirement.
  • Validation and Test Estimation: An estimation of the time and expertise required to carry on with the procedure.
  • Test Planning and Designing the testing environment: Based on the inputs from the estimation, an ETL environment is planned and worked out.
  • Test Data preparation and Execution: Data for the test is prepared and executed as per the requirement.
  • Summary Report: Upon the completion of the test run, a brief summary report is prepared for improvising and concluding.

ETL Testing Interview Questions

With the huge requirement for ETL testing, comes a huge requirement for experts to carry out these ETL testing process. Today, there are many jobs available for this process.

But only if you are well aware of the technical features and applications, you will have the chance of getting hired in this profile. You have to be well prepared on these basic concepts of ETL tools, their techniques, and processes to give your best shot.

Below you can find a few questions and answers which are more frequently asked in the ETL testing interviews:

Q #1) What is ETL?

Answer: ETL refers to Extracting, Transforming and Loading of Data from any outside system to the required place. These are the basic 3 steps in the Data Integration process. Extracting means locating the Data and removing from the source file, transforming is the process of transporting it to the required target file and Loading the file in the target system in the format applicable.

Q #2) Why ETL testing is required?

Answer: ETL testing is required

  • To keep a check on the data which are being transferred from one system to the other.
  • To keep track on the efficiency and speed of the process.
  • To be well acquainted with the ETL process before it gets implemented into your business and production.

Q #3) What are ETL tester responsibilities?

Answer: Responsibilities include

  • Requires in-depth knowledge of the ETL tools and processes.
  • Needs to write the SQL queries for the various given scenarios during the testing phase.
  • Should be able to carry our different types of tests such as Primary Key, defaults and keep a check on the other functionality of the ETL process.
  • Quality Check

Q #4) What are Dimensions?

Answer: Dimensions are the groups or categories through which the summarized data are sorted.

Q #5)  What is the Staging area referring to?

Answer: The Staging Area is the place where the data is stored temporarily in the process of Data Integration. Here, the data s cleansed and checked for any duplication.

Q #6) Explain ETL Mapping Sheets.

Answer: ETL mapping sheets contain all the required information from the source file including all the rows and columns. This sheet helps the experts in writing the SQL queries for the ETL tools testing.

Q #7) Mention a few test cases and explain them.


  • Mapping Doc Validation – Verifying if the ETL information is provided in the Mapping Doc.
  • Data Check – Every aspect regarding the Data such as Data check, Number Check, Null check are tested in this case
  • Correctness Issues – Misspelled Data, Inaccurate data and null data are tested.

Q #8) List a few ETL bugs.

Answer: Calculation Bug, User Interface Bug, Source Bugs, Load condition bug, ECP related bug.

In addition to the above ETL testing questions, there may be other vital questions where you may be asked to mention the ETL tools which you have used earlier. Also, you might be asked about any debugging issues you have faced in your earlier experience or about any real-time experience.

Hope, these basic getting started questions are helpful for your ETL testing interview.