In agile, accurate estimation of testing effort depends on a shared understanding of what “done” means. The Definition of Done (DoD) sets the minimum quality and completeness criteria for work to be considered finished—often including required testing types, code review, integration, documentation, and acceptance readiness. If the team cannot estimate testing, it frequently indicates inconsistent assumptions about required test depth, environments, automation expectations, or quality gates. Ensuring the DoD is understood first establishes a common baseline so the team can estimate consistently and make a realistic sprint commitment. Acceptance criteria (A) are important at the user story level, but they do not replace the DoD; a story can meet acceptance criteria yet still fail “done” standards if required tests or integrations are missing. Pair programming (B) may reduce defects but is not the first corrective action for estimation confusion. Adding a QA expert (D) can help, but without a shared DoD, expert input may still lead to mismatched expectations and unreliable commitments.