Change decorator returned by request_handler to return the handler function

[Exilit]

This allows to call the original function (e.g. to put it under test).
Otherwise the original function name gets bound to NoneType and is not
accesible anymore. (see https://stackoverflow.com/q/57349825/2980895)

Description

This pull request only adds a return handle_func to the wrapper function returned by SkillBuilder.request_handler(). The wrapper returned by this function is a decorator and therefore should return a function by convention.

Motivation and Context

The mentioned wrapper function does currently not return anything. Because of the logic of a decorator, the returned value of a decorator is bound to the original function name (see https://gist.github.com/Zearin/2f40b7b9cfc51132851a). Since the decorator does not return any value the original name is bound to NoneType.

As a result the function is not accessible anymore after decoration. This is not a big deal in general, as you should not need to call the function manually in most cases, but there are two reasons to change that:

1. To follow best practices.
2. To put the handler functions under test.

Currently it is not possible to unit test the handler functions, which results in lower code quality and also a more difficult development cycle.

Testing

The primary goal was to make the decorated handler functions testable. The success of the following test case verified the change in the first place:

from skill import some_handler
from tests import new_request

# tests.py

def test_intent():
    request = new_request('LaunchRequest', {'SlotName': 'slot value'})
    response = some_handler(request)

    expected_response = "abc"
    assert response == expected_response

# skill/__init__.py

from ask_sdk_core.skill_builder import SkillBuilder
from ask_sdk_core.utils import is_request_type

sb = SkillBuilder()

@sb.request_handler(can_handle_func=is_request_type("LaunchRequest"))
def some_handler(handler_input):
    return "abc"

To make sure, that this change does not break anything else, I ran the local unittests of the SDK, which finished successfully.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• I have extended existing tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[nikhilym]

This change is good. However, since we provide decorators across request handler, exception handler, request interceptor and response interceptor, it would be better to make the same changes across all these functions.

[Exilit]

You are absolutely right, i did not think about the other decorators before.
I will have a look into the other decorators and update this PR.

[Exilit]

@nikhilym I added the return statements to the other decorators aswell and extended the tests to make sure the returned function is correct.

[nikhilym]