Wherever possible, tests must be automated.
UnitTests, AcceptanceTests and RegressionTests must be AutomatedTests because FeedbackShouldBeFree. Asking other people to manually execute these tests for you is considered bad manners.
This is important because people can forget to run tests and it may take several days to get feedback from ManualTests. See RapidFeedback.
One often mentioned reason for not doing automated tests is that when an AutomatedTest fails, then all subsequent tests will fail because they are all based on the premise that the test that failed left the objects in a defined state, and that's no longer true because precisely the failed test failed.
So, no test should ever depend on other tests to succeed. All tests must be independent of each other.
See ManualTest AutomatedContinuousTesting ContinuousIntegration