I do understand there are some benefits, but I'm not convinced they outweigh the disadvantages (increased complexity, more code to glue everything together, which almost by definition increases the risk of breaking things).
>> a) Writing tests for the combined class is incredibly hard. Since you are relying on the UI framework to call your code you have very little control over when something happens (and what side effects it will cause).*
While this is definitely true, I fail to see how separating controllers and views helps to improve the reliability of your user interface code. Yes, it makes it easier to test individual parts of your UI code independently and without side-effects, but eventually all of it will end up on a user's device (that's the assumption, at least ;-), which means it has to 'rely on the UI framework' and 'has very little control over when things happen' anyway. If you are concerned about testing isolated parts of the UI code without side effects, it's probably better to factor them out into functions and test those directly.
>> b) Changing your code becomes a lot more time consuming. In an agile environment you want to be able to quickly change behavior and looks (sometimes even on the fly) which gets harder the stronger your coupling is.
I totally agree with this, but the question remains how many application developers face this scenario, and how the flexibility/complexity tradeoff scales for moderately complex user interfaces.
>> a) Writing tests for the combined class is incredibly hard. Since you are relying on the UI framework to call your code you have very little control over when something happens (and what side effects it will cause).*
While this is definitely true, I fail to see how separating controllers and views helps to improve the reliability of your user interface code. Yes, it makes it easier to test individual parts of your UI code independently and without side-effects, but eventually all of it will end up on a user's device (that's the assumption, at least ;-), which means it has to 'rely on the UI framework' and 'has very little control over when things happen' anyway. If you are concerned about testing isolated parts of the UI code without side effects, it's probably better to factor them out into functions and test those directly.
>> b) Changing your code becomes a lot more time consuming. In an agile environment you want to be able to quickly change behavior and looks (sometimes even on the fly) which gets harder the stronger your coupling is.
I totally agree with this, but the question remains how many application developers face this scenario, and how the flexibility/complexity tradeoff scales for moderately complex user interfaces.