I'm an Engineering graduate in Computer Science Engineering.
I want to build my career in ETL Testing.
What is the difference between ETL Testing and Development?
ETL basically stands for Extract Transform Load - which simply implies the process where you extract data from Source Tables, transform them in to the desired format based on certain rules and finally load them onto Target tables. There are numerous tools that help you with ETL process - Informatica, Control-M being a few notable ones.
So ETL Testing implies - Testing this entire process using a tool or at table level with the help of test cases and Rules Mapping document.
In ETL Testing, the following are validated - 1) Data File loads from Source system on to Source Tables. 2) The ETL Job that is designed to extract data from Source tables and then move them to staging tables. (Transform process) 3) Data validation within the Staging tables to check all Mapping Rules / Transformation Rules are followed. 4) Data Validation within Target tables to ensure data is present in required format and there is no data loss from Source to Target tables
Please visit these links http://etltestingguide.blogspot.com
In my experience, solely testing ETL isn't a viable career path. As Brent suggested, it would be a part of Business Intelligence but not normally something that can be done by itself.
In answer to your other question, ETL development would be creating the functionality that enables the Extract - Transform - Load process to work, whereas ETL testing would be ensuring that the process works as per the business requirements and producing the required data. Or, that's been the case at the places I've worked.
Hope this helps! Dan