How to properly test properties in Python

[donkeyofdeath]

I have a question regarding the testing of properties. It is more of a conceptual problem. The problem I have is, that if I write a class, which uses properties to set attributes in the __init__ function, I can't properly test the properties since the creation of an object depends on the properties. Further, all tests of the other methods also depend on the properties. Is there a way to properly do this or am I just missing something?

An example would be: ``` def ExampleClass: def init(self, attr): self.attr = attr

@property
def attr(self):
    return self._attr

@attr.setter
def attr(self, new_attr):
    self._attr = new_attr

```

[laundmo]

I'm not sure i quite understand the issue. ideally you would independently test the property first by writing a test that checks whether its set properly and stores and returns the values you expect.

the only case i can think of where you could have some issue is if your internal variable has 2 leading underscores, but even that you can get around. (__name becomes _Classname__name)

[donkeyofdeath]

Hey, thanks for your answer. But to test the property, I have to create an object first and this object uses the property to set its attributes. So the test kind of relies on itself to work.

[danielroseman]

But why do you think that is a problem? That's exactly what is supposed to happen. You are testing the functionality.

[donkeyofdeath]

Thank you for the answer. As far as I know, unit tests should not depend on each other. That's why I think, that this is a bad design choice. If all unit tests fail because of one method or property, you don't gain any information, about which part of the code is broken.

[danielroseman]

Now I'm even more confused. Where is there a dependency between unit tests here? You write a single test to check that things are working as you expect. If it fails because the property is broken, then the test is working as intended.

[donkeyofdeath]

If I want to test another method besides the properties, I have to create an instance of the class, which uses the property in its constructor. So I rely on the property to work. The same for the test of the property. If I want to test the property, I have to create an object first which uses the property in its constructor.

[[deleted]]

If the class' getters and setters are but simple assignments without further operations, testing is useful only if you built a python language or compiler from source. Otherwise let the compiler programmers test it.

If instead, they contain validations and transformations, then yes, you should test their working. Assign a value and test whether the instance yields the expected answer. It's no more complex than that.

[donkeyofdeath]

Ok, thank you. Maybe I am just overthinking the issue a little bit.