Error is human it is the fact that drives the need for automation testing. Because manual testers may not run test cases correctly. There will be a lot of chance of making mistakes. They may provide incorrect input data due to a typographical error, or may not be aware of the actual behavior of the system correctly, or may not report the test result correctly, or may not run some test cases, or may be forget to run some. preconditions, or they can change the sequence of execution of the test case in case the sequence is important.
Another important factor is that the automation test scripts will be used as a way to store the domain / project / task knowledge acquired by the test engineers. Say, for example, if a Tester works on a project for a year, he could have spent more time learning the domain, the purpose of the project, the modules of the project, the flow of all functionalities. You will be familiar with known issues and challenges.
If this Tester leaves the project, the knowledge acquired by him will also go away.
It is very difficult for the newly recruited Tester to understand the entire content of the Test Case document.
If the automation test scripts are already available, then the new Tester can simply start the test by running the automation scripts, without getting much knowledge about the project.
You can understand the flow / data by watching the automation test scripts run. But anyway, you should gain domain / project knowledge to further improve / update the automation scripts. So, we can say that test automation is a way of storing knowledge.
Automation tool like QTP (Quick Test Professional) has a function to store screenshots of each and every page browsed during execution. So it can be used as proof for testing completion, and we can also refer to the screenshots of previous runs if there is a need to refer to them.
The test report can be automatically written to a custom report page which will ensure the accuracy of the report and can also improve the appearance of the report.
The most important advantage of automation tests over manual tests is the speed of execution. The test run can be completed quickly and we can also run the scripts overnight as well without human involvement. So ultimately, the total time required for testing can be reduced, which will help significantly to complete the project on time. Some tests may need to be done at a specific time. It can be easily achieved by running those automation test scripts in an elder job / task scheduler. Tool like QTP supports automation object model to achieve this.
Functional test automation scripts will also be useful for performance testing. Because many performance testing tools will support reuse / invocation of these test scripts.
Some kind of test involves comparing a large amount of data between the previous version and the current version as part of the regression test. It may practically not be possible to do it manually. This problem can be easily solved by a simple shell script or any other script like vbs, wsh.
Because automation test tools support data-driven testing, test execution can be performed repeatedly with many different data sets.
There are many automation testing tools available for functional, regression, and performance testing. Test complete, SilkTest, SilkPerformer, QARun, QALoad, TestPartner, WinRunner, LoadRunner, QTP, Rational Robot and openSTA are some of them. QTP is more widely used now as it supports vbscript and can be used to test many different applications simply by adding the required plugins.