Closes #762: Fixes off by one error in Segemented array peel method.

[glitch]

Closes #762

• Fixes off by one error in Segemented array peel method.
• Updates Strings.peel unit test to check that bytes pdarrays are appropriately structured with respect to null bytes.

[reuster986]

I'm not familiar enough with pytest to know this, but does self.assertEqual(list1, list2) actually do the element-wise comparison and check that they are all True? To me, I would be wary that it is just calling assert list1 == list2 under the hood, which would produce the wrong result (or an error).

Elsewhere, I have been using self.assertTrue((arr1 == arr2).all()) with either numpy arrays or arkouda arrays to ensure all the element-wise comparisons are happening, but if assertEqual does the right thing with python lists, I would be interested to know.

[glitch]

That's a good question, I'm fairly certain python's unittest.TestCase (where the assertion methods are coming from) really default down to the operator methods, so assertEquals(a, b) delegates to a == b which is an equivalence test vs a is b which is same ref.

I ran the following in a python console to double check
Gist here

x = ["a", "b", "c"]
y = ["a", "b", "c"]
z = ["c", "b", "a"]
x == y
> True
x is y
> False
x == z
> False

import unittest
t = unittest.TestCase()
t.assertEqual(x, y)  # passes
t.assertTrue(x is y) # fails
t.assertEqual(x, z)  # fails

# There is also a assertListEqual(a, b) which may be a bit more explicit
t.assertListEqual(x, y)  # passes
t.assertListEqual(x, z)  # fails

So while it's testing the correct thing, I think I'll push an update to improve clarity with assertListEquals

[glitch]

Note: I don't have a link to the python src handy, but for 3.7.9 unittest / case.py _baseAssertEqual the code is this

    def _baseAssertEqual(self, first, second, msg=None):
        """The default assertEqual implementation, not type specific."""
        if not first == second:
            standardMsg = '%s != %s' % _common_shorten_repr(first, second)
            msg = self._formatMessage(msg, standardMsg)
            raise self.failureException(msg)

so it is basically python's == function, we should be good with either assertEqual or assertListEqual

[reuster986]

Ah, ok. I guess I had confused the behavior of python lists with numpy arrays and had forgotten that a == b will work with the former.

Side note: if a and b are numpy arrays (or arkouda arrays), a == b will return a bool array the same length as a and b with the result of each element-wise comparison, instead of a single bool value. So calling assertEqual(a, b) will raise a ValueError error saying "the truth value of an array is ambiguous" or something like that. Not a problem for python lists, but something to watch out for when writing unit tests on numpy/arkouda arrays.