Issue Type: Bug

Visual Studio Code doesn't support attribute @expectedfailure, which used for python testsing framework unittest

@expectedFailure
def test_expected_error(self):
   ...

VS Code version: Code 1.39.2 (6ab5985, 2019-10-15T15:35:18.241Z)
OS version: Windows_NT x64 6.1.7601
Python 3.6.3 |Anaconda custom (64-bit)| (default, Oct 15 2017, 03:27:45) [MSC v.1900 64 bit (AMD64)] on win32

microsoft/vscode#84050 (comment)