A test script in software testing is a set of instructions that will be performed on the system under test to test that the system functions as expected.
There are various means for executing test scripts.
These last two types are also done in manual testing.
The major advantage of automated testing is that tests may be executed continuously without the need for a human intervention. Another advantage over manual testing in that it is faster and easily repeatable. Thus, it is worth considering automating tests if they are to be executed several times, for example as part of regression testing.
Disadvantages of automated testing are that automated tests can — like any piece of software — be poorly written or simply break during playback. They also can only examine what they have been programmed to examine. Since most systems are designed with human interaction in mind, it is good practice that a human tests the system at some point. A trained manual tester can notice that the system under test is misbehaving without being prompted or directed however automated tests can only examine what they have been programmed to examine. Therefore, when used in regression testing, manual testers can find new bugs while ensuring that old bugs do not reappear while an automated test can only ensure the latter. That is why mixed testing with automated and manual testing can give very good results, automating what needs to be tested often and can be easily checked by a machine, and using manual testing to do test design to add them to the automated tests suite and to do exploratory testing.
One shouldn't fall into the trap of spending more time automating a test than it would take to simply execute it manually, unless it is planned to be executed several times.