Clark did not believe such moves would green-light drug use.
"In my experience, the state of the law is almost irrelevant as to whether people use drugs or not. My motivation is, how do we stop death, how do we support wellbeing?"
Clark was a speaker at a gathering of addiction sector leaders at Parliament today. Late last year she was appointed to the prestigious Global Commission on Drug Policy, a drug reform think-tank.
Drug Foundation executive director Ross Bell welcomed her support for injecting rooms and drug-testing.
"Having the mana of Helen Clark on an issue that is so politically sensitive and treacherous, she's able to bring her leadership and say these things which New Zealand finds difficult," he said.
Kathryn Leafe of the New Zealand Needle Exchange Programme said it was important to enhance harm reduction and there was plenty of evidence that drug-testing and injecting rooms did this.
"I was really heartened by many of Helen Clark's comments and also her support for the needle-exchange programme."
The Drug Foundation and other organisations already carry out testing at festivals, but it is a legal grey area.
Recently, drug-testing body KnowYourStuffNZ discovered the dangerous pain-control drug Fentanyl at a New Zealand music festival. The potent drug has killed dozens of people overseas.
Police also issued a warning last month when 13 people became ill after taking what they thought was ecstasy but was later found to be a much more potent drug.