The controller code as originally written, with a small test suite

controller1.py

import pytest

def product_index(request):
    limit = request.GET.get('limit')
    offset = request.GET.get('offset')

    if limit and limit.isdigit():
        limit = int(limit)
    else:
        limit = 10

    if offset and offset.isdigit():
        offset = int(offset)
    else:
        offset = 0

    return limit, offset


class MockRequest:
    def __init__(self):
        self.GET = {}

def test_pytest_is_correctly_installed():
    assert True == True

def test_default_values_when_no_parameters_given():
    request = MockRequest()

    (limit, offset) = product_index(request)
    assert limit == 10
    assert offset == 0

def test_values_coerced_to_int_when_string_params_given():
    request = MockRequest()
    request.GET['limit'] = '20'
    request.GET['offset'] = '50'
    
    (limit, offset) = product_index(request)
    assert limit == 20
    assert offset == 50

def test_default_returned_when_param_is_unparseable():
    request = MockRequest()
    request.GET['limit'] = 'qwerty'
    request.GET['offset'] = '50'

    (limit, offset) = product_index(request)
    assert limit == 10