Analyze business requirements, functional specifications, and technical designs to develop comprehensive test scenarios and test cases.Perform functional, system, integration, regression, and end-to-end testing of mainframe applications.Validate COBOL programs, JCL/batch jobs, DB2 data, CICS transactions, and VSAM files.Execute batch cycles and verify job outputs, return codes, file/database updates, and downstream processing.Perform backend data validation using DB2/SQL queries.Identify, document, track, and retest defects using Jira, Azure DevOps, or ALM/Quality Center.Conduct root-cause analysis of test failures using job logs, spool outputs, datasets, and database records.Prepare test cases, test data, execution evidence, defect reports, and test completion reports.Collaborate with developers, business analysts, product owners, and upstream/downstream application teams.Participate in Agile ceremonies, test planning, estimation, status reporting, and release-readiness activities.