Merge Sort Algorithm Python
Reduce nesting

If you invert the condition if len(list) &gt; 1: near the beginning and use an early return,
you can reduce the level of nesting, making the code slightly easier to read:

if len(list) &lt;= 1:
    return list

middle = len(list) // 2
left_sorted = mergeSort(list[:middle])
right_sorted = mergeSort(list[middle:])
# ...


Eliminate k

The variable k is unnecessary, as it will never reach len(list). You can delete it and all its uses.

Style

The implementation doesn't follow recommended conventions of naming and formatting. I suggest to read and follow PEP8.

The good

It's really great that you included unit tests,
it made the review easier :-)