I’ve been exposed to Agile/Scrum for a while and recently I tried to summarize some testing principles which are all concerned with quality.
Test Driven
- Test cases and unit test will be developed prior to coding any lines
 - Unit test will be required to ensure the quality of the refactoring
 
Test Early
- Deliverables in each sprint/iteration will be tested in a timely manner
 - Customer will never be surprised in the last minute due to the incremental testing efforts in each sprint.
 
Test Often
- Continuous integration will be employed to test against each successfully build
 - Tests will be executed basing on sprint or iteration.
 
Test Unattended
- Build automation will be performed overnight
 - Automated testing will be leaveraged
 - Report will be automatically pushed to stakeholders
 
Test Completely
- code coverage will be introduced to ensure the coverage of your tests
 - traceability between test assets and source code will be established
 - regression tests will be conducted timely (through automated most likely)
 
Test Comprehensively
- Strict coding guidelines will help developer to code in a more secure way.
 - Performance/load testing will be conducted to ensure the deliverables are reliable
 - Static code examination will reduce the risk of security.
 
