I just read the concept concerning Equivalence Class Partitioning and Boundary Value Analysis and I'm wondering if it can be applied to other test cases For example clicking on a button, choosing values from a dropdown, etc... And if yes how will it be applied in such cases
Equivalence Class Partitioning is usually demonstrated using numerical values since it is easier to understand and apply, but I don't see any reason not to extend it further to any values that are related in any way. ECP can work great on variable that has a "type" or Belonging, for example type of a car- you can group micro and super mini's and SUV's with pickups or type of the fruit- group all the Citrus together, all the berries and all the apples.
The car example above is somewhat related to a measurable attribute- the size of the car, or Belonging like the fruit's family but ECP can work even on attributes- group all the pink and red shirts, the blue and purple then the black and white.
Boundary Value Analysis by definition relates to sequences, but it is not limited to numerics- you can check the boundary of the alphabet, the biggest and smallest car (although this is actually quantitative by weight for example) or the most beautiful and ugliest people in your "AI beautifier" tests
Equivalence Class Partitioning helps you determine that in a field which asks "enter a integer" you know that entering all numbers 1-100 would give the same result (more or less). You can also state that entering a good user name and bad password is the same as entering a bad username, as both result in the same output; "Invalid username/password."
Boundary Value Analysis helps you determine that if a SQL column is NVARCHAR(100) that we can put in 123 characters and see what happens. In that way there are valid zones (ranges) of data and invalid ones.