..
----------------------------------------------------------------------
Ran 2 tests in 0.005s

OK
(command.Simple
  blame_tok:(Token
    id:Lit_Chars
    length:4
    col:0
    line:(SourceLine
      line_num:1
      content:"echo _{a,b}_"
      src:(source.MainFile path:"<cmd_eval_test.py>")
    )
  )
  more_env:[]
  words:[
    (CompoundWord parts:[...0x7f8b7918c870])
    (word.BracedTree
      parts:[
        (Token id:Lit_Chars length:1 col:5 line:...0x7f8b7919c470)
        (word_part.BracedTuple
          words:[
            (CompoundWord
              parts:[(Token id:Lit_Chars length:1 col:7 line:...0x7f8b7919c470)]
            )
            (CompoundWord
              parts:[(Token id:Lit_Chars length:1 col:9 line:...0x7f8b7919c470)]
            )
          ]
        )
        (Token id:Lit_Chars length:1 col:11 line:...0x7f8b7919c470)
      ]
    )
  ]
  is_last_cmd:F
)

[(Piece s:"" quoted:F do_split:T)
]
[(Piece s:xxx quoted:F do_split:T)
]
[(Piece s:default quoted:F do_split:T)
]
[(Piece s:xxx quoted:F do_split:T)
]