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I think you don't understand what unit testability means. It means removing IO and side effects from your code. How the hell do I test a print function? I take

• Marazan 3y ago
  blink Of course you can make the function with a print statement more unit testable without completely changing it's semantics! You pass in an outputstream and use that as the target for print. Then your unit test can create its own stream and test the content of the stream whilst production code can pass in standard out. That way you don't completely change the semantic meaning of the code. And once again that GPT function is useless. It is identical to list(range()) and it doesn't do what the first function does. Anyone can make anything more unit testable if it doesn't have to do the same thing.
  • byby 3y ago
    Bro, dependency injection and mocking is the same thing as segregating your function from IO. Your replacing io calls to stdout with io calls to something else. But that doesn't make your code unit testable. The function is still touching io. You gonna test it with another function that touches io? That defeats the point of the definition of unit testability. > and doesn't do what the first function does. Are you serious? You mock your output streams with hacky monkey patching your function ALSO stops doing what it originally does. It's essentially black magic globals that mutate your program... very bad practice. Chatgpt here just didn't write the obvious io component of the code because it would be freaking pedantic. The full code would include a function that prints lists composed with a function that produces lists. The composition allows part of the program to be testable while leaving the io part of it not testable. For the original program NONE of it was testable. Your Monkey patching here would be replaced by different io functions. You want to change the output stream? then you change the IO function. Compose the list producer with another IO function. Play type Tetris and you can recompose your list producing function with all kinds of modular io. The point it you separated the core logic away from IO thereby making it more modular and more testable. None of the io functions are testable via unit tests, that is the point. That is the definition of the most basic form of testing... Unit tests. You literally HAVE to change your code in order to make it unit testable. If your code is throwing shit to io and retrieving values from io then none of your code is unit testable. You're at the integration test level and at this level things become hacky and more complicated. Your tests not have external dependencies like state, the operating system and you have to run hacks like your monkey patch. Where ever you work or whatever you've been doing if you haven't been doing what I described then you (and your work buddies) haven't been testing your code via unit tests. That's fine, whatever works bro. But chatGPT knows the common parlance for testing and unit testing, and it did exactly the correct thing. Your interpretation of what testing is the thing that is strange and off here.
    • Marazan 3y ago
      I'm sorry, I clearly haven't explained myself well as otherwise you would not have wasted a huge amount of text tying yourself in knots based clearly on a mistaken apprehension of what I was saying. For clarity I reproduce the original function you gave and then I present what the change I am suggesting is def cool_function(x): for i in range(x): print(i) My change def cool_function(x, output_stream=sys.stdout): for i in range(x): print(i, file=output_stream) Does it now become clear what I am suggesting? My new function can be used as a 1-for-1 replacement for the old function, no code of the system needs changed as the default value provided to the new variable ensures semantically identical operation without changing any further code. Yet it is now unit testable But now we can write a unit test like def test_output(): output = io.StringIO() cool_function(1, output) contents = output.getvalue() assert contents=="1\n" So I've made the code unit testable, kept semantics completely identical and not had to worrty about any weird IO concerns that you have. No monkey patching, no weird file IO, no bizarelly re-implemnting list(range(x)).
      • byby 3y ago
        > I'm sorry, I clearly haven't explained myself well as otherwise you would not have wasted a huge amount of text tying yourself in knots based clearly on a mistaken apprehension of what I was saying. No need to apologize. This is a discussion. No one did anything wrong. >For clarity I reproduce the original function you gave and then I present what the change I am suggesting is This is called dependency injection and it's a valid way of segregating IO away from pure logic. Although this pattern is popular among old school OOP programmers it's getting out of vogue due to the complexity of it all. You used a python trick here of default values, but typically dependency injection changes the function signature and ups the complexity of the code by a lot. Let me show you the full output of the code that chatgpt was implying: #unit testable code (without using dependency injection tricks) def cool_function(x: int) -> None: IO_function(logic_function(x)) def logic_function(x: int) -> List[int]: return [i for i in range(x)] def IO_function(x: Any) -> None: print(x) def test_output(): assert logic_function(4) == [i for i in range(4)] Chatgpt only gave you logic_function, because IO_function is sort of obvious.. it's just "print" (I only wrapped print in "IO_function" to keep things clear, typically you won't define that function). But basically the full complete code would be to recompose IO with logic. You now have two components one of which is testable. As a side note you will see it's actually an improvement to the code. It's simpler, no dependency injection, no confusing function type signature and a much simpler test case. The other thing that must be noted is the modularity. Making tests unit testable in this way allows for your logic to be portable. What if I want to repurpose cool_function to output it's logic to another function? In your example you don't have the components to do that, it's harder for your case as you'd have to create another component for injection. In short not only did chatGPT produce A correct answer. But it produced the better answer compared with your dependency injection. That being said your dependency injection is valid BUT you were not correct in saying that chatGPT's answer was worse or incorrect.
• wizofaus 3y ago
  That would be fine if the core thing needing unit testing was the data generation/ transformation logic, but just as often as not it's the output formatting too. Did you try asking ChatGPT to write a unit test to confirm that the output is displayed as expected?
  • byby 3y ago
    >That would be fine if the core thing needing unit testing was the data generation/ transformation logic, but just as often as not it's the output formatting too. Output formatting touches io. In this case it is no longer a unit test that touches these things. Unit tests by definition test ONLY internal logic and transformations. It is literally the definition of unit tests. When you test things like stdout that becomes an integration test and Not a unit test. It requires some external thing or some global black magic monkey patch that changes what print does to do integration testing. (Btw making print formatting unit testable means segregating the formatting from the print. Produce the string first, test that, then print, because print can never be unit tested by definition) Typically programmers segregate these levels of testing because unit tests are easier to write. But to write unit tests your code has to be written in a way to cater to it. Often this style of coding actually improves your code it makes it much more modular. The reason is because pure functions that output data can be composed with all kinds of io functions. You can move it all over the place and to different platforms with different forms of IO. Print has no meaning in certain embedded systems so it can't be moved... By segregating the logic out it makes it so I can move the logic without the io baggage. Chatgpt 100 percent gets the difference that's why it did what it did. I think you and the OP don't fully understand the meaning of unit testing. Don't take this the wrong way, but just because you don't know this doesn't say anything about your skills as a programmer. But just recognize that this concept is basic and is pretty much something universal among testing.
    • wizofaus 3y ago
      > Unit tests by definition test ONLY internal logic and transformations Output formatting is still a type of transformation! The function explicitly takes the numbers and prints them as decimal integers with newlines between each. A test to confirm that it IS in that format is still a unit test. BTW I gave ChatGPT the prompt I would give, and I have to say the answer looks pretty good, even if I'm not a Python programmer and it's not the way I'd do it (which would be to change the function to allow passing in an output stream): class MyFunctionTestCase(unittest.TestCase): def test_my_function(self): expected_output = "0\n1\n2\n" with patch('sys.stdout', new=StringIO()) as fake_out: my_function(3) self.assertEqual(fake_out.getvalue(), expected_output) With a few more prompts I also managed to get it give me this version: def my_function(x: int) -> str: output = "" for i in range(x): output += str(i) + "\n" return output Which I'd argue somewhat changes the code that was originally written, but it's still a pretty decent answer. There's no doubt there's some impressive stuff going on that it can do such things, the real issue for me is that when I've tried on far more complex functions it's tended to break down (quite badly in some cases).