CRJ-200 Captain reported during taxi out they received hydraulic system and steering malfunction messages. Flight crew contacted maintenance and were towed back to the gate.

Narrative

Previous crew wrote up stall fail caution and did not contact MX. I contacted Mx and asked about the time frame for RTS and decided to board. With passengers on board Mx preformed stall test and it shut down the apu with passengers on board. We then restarted the airplane and MX preformed stall test again with out incident and I informed the passengers that due to a Mx issue from previous flight we had shut the plane down. Mx then returned the plane to service and we completed required tasks and pushed off gate without issue. On taxi out we got hydraulic 3 low pres and hydraulic system 3 high temp and steering inop. We ran associated QHR's and contacted Mx. they informed us we needed to be towed back to gate. Tow team informed us that we were leaking hydraulic fluid and the airport equipment was dispatched to us. Mx then cleared us to be towed and we were towed back to gate. Cause: Potential contributing factor would be improper shutdown while maintenance doing stall test while passengers were on board. Suggestions: Better coordination between crew and Mx regarding non standard shutdown/ termination of aircraft and potential ramifications of this.