I need to do test to see if a command block has succeeded but the command in the commandblock does not emit a comparator signal!
Command blocks are of Tile Entity type "Control". According to the wiki:
Control has these additional fields:
- Command: The command to issue to the server.
- SuccessCount: Represents the strength of the analog signal output by redstone comparators attached to this command block. Only updated when the command block is activated with a redstone signal.
- LastOutput: The last line of output generated by the command block. Still stored even if the gamerule commandBlockOutput is false. Appears in the GUI of the block when right-clicked, and includes a timestamp of when the output was produced.
- TrackOutput: 1 or 0 (true/false) - Unknown.
Since your command does not yield a redstone signal, the only way to detect the outcome of the command block via data tags is to read LastOutput.