string mutation causes UnicodeDecodeError

[golankai]

I am working on a project that includes text normalization and using mutmut for mutation testing.
mutmut is mutating line 35 to be normalized = 'XXXX' instead of normalized = ''

I then get the following error:

when I run my tests regularly they work, and when I apply this change manually and run my tests, they work too.

Have any Idea what can happen that causes this failure?

[boxed]

Are you sure this is the mutation that fails? Is that what you get with mutmut show 0?

"position 35" in the error would be the column 35, not the line 35 of the file.

[golankai]

the position is indeed 35, but coincidently also the row I referred to :) when reporting the error, the position changes, as it is using a random string from Hypothesis testing.
I am sure.

1. Running the tests themselves produces no error.
2. Applying the mutation manually and running the tests produces an assertion error (this is good) but not a fatal Error of 'utf-8'.
3. running mutmut run crashes as I showed above, and then also by running mutmut run 4 (4 is the id of this mutant).

This is quite weird. I have seen before in our project those errors that comes from normalization, but I don't get how and why this mutant causes them, only when running through mutmut.

[boxed]

Weird. You could add a print(repr(line)) in the mutmut code.