test: Added test_026_validate_bad_request_response_format

[viniarck]

Closes #217

Summary

Added and augmented test to cover bad request response format since @validate decorator implementation will change and is being moved.

Local Tests

+ python3 -m pytest tests/ -k test_025_should_fail_due_to_invalid_attribute_on_payload
============================= test session starts ==============================
platform linux -- Python 3.9.2, pytest-6.2.5, py-1.11.0, pluggy-1.0.0
rootdir: /tests
plugins: timeout-2.0.2
collected 224 items / 223 deselected / 1 selected

tests/test_e2e_11_mef_eline.py .                                         [100%]

------------------------------- start/stop times -------------------------------
========== 1 passed, 223 deselected, 51 warnings in 79.56s (0:01:19) ===========

+ python3 -m pytest tests/ -k test_026_validate_bad_request_response_format
============================= test session starts ==============================
platform linux -- Python 3.9.2, pytest-6.2.5, py-1.11.0, pluggy-1.0.0
rootdir: /tests
plugins: timeout-2.0.2
collected 224 items / 223 deselected / 1 selected

tests/test_e2e_11_mef_eline.py .                                         [100%]

========== 1 passed, 223 deselected, 51 warnings in 76.04s (0:01:16) ===========

End-to-End Tests

No need to rerun the entire suite, local tests were run covering the changes.

[viniarck]

I'll go ahead and merge this.