mutmut and @property

[ljd42]

Hi there,

During my last Python class, one participant discovered an interesting case with @property, which I reproduced and simplified below.

"""demo mutmut issue with @property"""

class A:
    def __init__(self, value=0):
        self.x = value

    @property
    def x(self):
        return self._x

    @x.setter
    def x(self, value):
        if isinstance(value, (int,float)):
            self._x = value
        else:
            raise TypeError

mutmut is reporting one survivor:

• the mutation that removes the @property decoration

Now I am wondering. Applying the mutation causes a Syntax Error, whence the test suite does not run at all.

Does that count as survived? Or are we supposed in this case to suppress the mutation with a #pragma?

Thanks in advance,
Loic.

[boxed]

If it's a syntaxerror it should have failed the test run, and that should have caused the mutation to be marked as killed.

[ljd42]

Hi Anders,

Unfortunately, it doesn't :( One mutant survives (3), diff below:

PYTHONPATH='./src' mutmut show 3
--- ./src/issue.py
+++ ./src/issue.py
@@ -4,7 +4,6 @@
     def __init__(self, value=0):
         self.x = value
 
-    @property
     def x(self):
         return self._x

If I apply the mutation and re-run the test suite manually:

PYTHONPATH='./src/' pytest
============================= test session starts ==============================
platform linux -- Python 3.10.7, pytest-7.1.2, pluggy-1.0.0
rootdir: /home/loic/oss/issue_mutmut
plugins: cov-3.0.0
collected 0 items / 1 error                                                    

==================================== ERRORS ====================================
_____________________ ERROR collecting test/test_issue.py ______________________
test/test_issue.py:2: in <module>
    from issue import A
src/issue.py:3: in <module>
    class A:
src/issue.py:10: in A
    @x.setter
E   AttributeError: 'function' object has no attribute 'setter'
=========================== short test summary info ============================
ERROR test/test_issue.py - AttributeError: 'function' object has no attribute...
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
=============================== 1 error in 0.15s ===============================

Happy to provide further information later on if required.

[ljd42]

Just had a quick look at the code... I might have a clue about the issue.
In __init.py:tests_passed() returns true if returncode != 1.

Because the test fails due to an uncaught exception, in this particular case the return code will be 2 (On Unixoide at least. TBD on Windows).

[ljd42]

Unfortunately, I couldn't enter pdb by adding breakpoint() before the above line. So, I switched back to a simple print statement.

Hypothesis confirmed:

2. Checking mutants
⠸ 0/5  🎉 0  ⏰ 0  🤔 0  🙁 0  🔇 0*** returncode =1
⠸ 1/5  🎉 1  ⏰ 0  🤔 0  🙁 0  🔇 0*** returncode =1
⠴ 2/5  🎉 2  ⏰ 0  🤔 0  🙁 0  🔇 0*** returncode =2
⠸ 3/5  🎉 2  ⏰ 0  🤔 0  🙁 1  🔇 0*** returncode =1
⠇ 4/5  🎉 3  ⏰ 0  🤔 0  🙁 1  🔇 0*** returncode =1
⠏ 5/5  🎉 4  ⏰ 0  🤔 0  🙁 1  🔇 0