Database testing involves validating that database operations produce the correct results according to requirements. This includes ensuring data accuracy, proper handling of insertions/deletions/updates, and that the database schema correctly models real-world data. Key aspects to test include data mapping between the user interface and database, adherence to ACID properties like atomicity and isolation, data integrity across interfaces, and conformity to business rules using techniques like constraint and trigger testing. Thorough database testing from the early stages is important for complex systems, as backend/database bugs could cause whole projects to fail.