An RTM is a document that maps requirements to their corresponding test cases (and often defects), ensuring every requirement is covered by tests and providing bidirectional traceability between requirements and testing artifacts.
The RTM links each requirement ID to the test case IDs that verify it, so you can prove COVERAGE (every requirement has at least one test) and perform IMPACT ANALYSIS (if a requirement changes, which tests are affected). Forward traceability maps requirements → test cases; backward maps test cases → requirements; bidirectional does both. It surfaces gaps (requirements with no tests) and orphan tests (tests with no requirement). RTM is a key quality-gate artifact, especially in regulated domains, and answering 'how do you ensure full requirement coverage?' with RTM demonstrates process maturity.
An RTM shows requirement REQ-12 (password reset) is covered by TC_45–TC_49; when REQ-12 changes, the team instantly knows those five tests need updating — and spots that REQ-15 has no test yet.
How do you ensure every requirement has been tested, and how does that help when a requirement changes?