Hi,
You have two option to set transactions in TC.
Using the built-in UI transactions or the LR JS API.
If using the UI transactions they are set to AUTO so they will fail/pass according to the contained steps within.
Pay attention that we had a defect in prior versions with this mechanism, it was solved for LR 12.00.
If using the LR JS API you can add an evaluate JS step and call LR.startTransaction/LR.endTransaction functions in which you can set the status as a parameter.
Read more in LR documentation about the exact usage.