PyFile:TrailingCommaInArgList.py
  PyFunction('some_function')
    PsiElement(Py:DEF_KEYWORD)('def')
    PsiWhiteSpace(' ')
    PsiElement(Py:IDENTIFIER)('some_function')
    PyParameterList
      PsiElement(Py:LPAR)('(')
      PyNamedParameter('a')
        PsiElement(Py:IDENTIFIER)('a')
      PsiElement(Py:COMMA)(',')
      PsiElement(Py:RPAR)(')')
    PsiElement(Py:COLON)(':')
    PsiWhiteSpace('\n    ')
    PyStatementList
      PyPassStatement
        PsiElement(Py:PASS_KEYWORD)('pass')