You have to think and run your test scenarios like a real user/customer!

I wanted to buy a book on Amazon. I was not sure about the cost and time of delivery but i needed asap and in my budget. I browsed the similar books and compared prices and popularity of the author. The price was on higher side as these were printed books and delivery time was also around a week. Then i checked digital editions of these books which were not expensive and were also available on all my devices immediately. I browsed some of the eBooks and purchased one of them. I paid using my credit card and the book was available for me to read on my laptop.

Check the above scenario created by a real time user while making a purchase on a online store. check the amount of time spent by the user for executing this scenario. Amazon worked fine and there were no errors. I was a happy customer. Can you cover this scenario while writing test cases/scripts? May be, No.

My point is, while going through the requirements documents, make sure to understand the real use of the software. How this is going to be used? How different functionalities/modules are going to interact? If you can cover these in your test scripts, nothing better than that. However, you need to be creative, focused, and use software tester's brain to get closer to the expected scenarios that can be created by the real user.

As you can not ask for unlimited amount of test time, You need to make sure that type of test execution done by you is measurable and metrics can be produced.