A DB testing developer is responsible for validating and ensuring the integrity of data in databases. They create and implement test plans, perform various types of testing like functional, system, regression, and load testing on databases. They also detect, track, and rectify data inconsistencies or anomalies. Their role involves writing complex SQL queries and scripts to manipulate data for testing purposes. They also collaborate with other developers to design and optimize databases. It's crucial for them to ensure the security, reliability, and accuracy of data, and they play an essential role in maintaining the quality of software applications.