99% of the work in testing is coming up with test scenarios and test cases. 95% of the code is just dealing with setting up input and output data, 4% is calling the code you want to test and the final assert is often just a single line of code.

I'm not sure what depth of experience has to do with any of this, since it is busy work that costs a lot of time. A form with 120 fields is a form with 120 fields. There is no way around coming up with the several dozens of test cases that you're going to test without filling out almost all of the fields, even the ones that are not relevant to the test itself, otherwise you're not really testing your application.