Generally, if you do any work, whether or not you expect to be paid, you are treated as capable of work for the week in which you do the work (Sunday to Saturday) and so are not entitled to:

If you come off ESA to start paid work, you can protect your right to return to the benefit for up to 12 weeks (see below).

If you start paid or voluntary work, this is not in and of itself a reason for the DWP to trigger an ESA work capability assessment reassessment. The DWP can, however, arrange a reassessment if the particular nature of the work suggests that your physical or mental condition has changed.
ESA Regs, regs 15(9) & 30(5A)

You are allowed to do the kinds of work described below while remaining on ESA or NI credits, although that work might not be ignored completely. The sort of activi