A lot depends on the stored energy, which will be represented by the product of the volume and pressure. It will also depend on the material from which the receptacle is made. If it is glass, I would not be using mesh, for instance.

A good place to start is the HSE publication GS4

http://www.hse.gov.uk/pubns/gs4.htm

When undertaking a pressure test ensure hydraulic hoses are suitably rated usually1.5/2 the test pressure.
It is common practice to have a pressure gauge or pressure recorder to establish when test pressure
has been reached, there also must be a safe method of venting the trapped pressure.
I hesitate to say more as I am unsure what you are actually testing, (vessel ,piping etc).
If there is any insurance involved it may have to be witnessed by third party or recorded
over a certain time period (ie 1 hour). If the pressure falls on gauge you might then resort to
a leak test-( soapy water).
Nitrogen is commonly used to test items such a pressure switches.

bring in a competent person and learn from them so next time you are better armed

As per earlier responses, it's wise to use liquids (fluids) for pressure testing wherever possible. This comment stems from sporadic experiences during my time with HSE:

Not long after I joined HSE one of my experienced colleagues investigated and successfully pursued a prosecution for an accident in which an industrial heat exchanger ruptured during pneumatic pressure testing. I think the highly distorted casing of the exchanger was produced in court in order to help the judge and others present to understand the degree of force suddenly unleashed by the rupture and why the firm being prosecuted should have used hydraulic testing.

At another time, a colleague and I had some involvement with one or more companies which maintained and tested hyperbaric (high pressure) chambers used on oil platforms by divers before and after diving under compression. Such chambers are also used in medicine for treating divers with decompression sickness and other purposes such as hyperbaric oxygen therapy (HBOT) for acute conditions such as carbon monoxide poisoning and, somewhat debatably, for chronic conditions such as cerebral palsy and multiple sclerosis. The companies involved provided various reasons why hydraulic testing was not reasonably practicable for the periodic re-testing of chambers containing equipment and other fittings. Therefore, with the support of specialist engineering inspectors, agreement was given to pneumatic testing provided that a safe system of work was used, i.e. locating each chamber to be tested in either a pit or open-topped blast enclosure surrounded by a sizeable zone from which people could be excluded and in an area sufficiently remote to avoid harm to anyone if a chamber did explode during testing. Such testing would be controlled by suitably qualified people located in a suitably remote or protected bunker and using closed circuit television (CCTV), etc.

Several years into my time with HSE the group I was in had to inspect a selection of lighthouses - one of the more unusual types of workplaces/employment which only became subject to OS&H legal requirements in the UK after the arrival of the HSW Act 1974. At that time a common feature at many lighthouses was a large foghorn. Each foghorn produced a loud low frequency noise with a duration and interval specific to its location, and required a significant supply of compressed air. In order to ensure that such a supply was available whenever needed, lighthouses had very large air receivers - strong specialised tanks - used for storing copious amounts of compressed air produced by one or more compressors. Though the standard of maintenance of lighthouse buildings and equipment was generally found to be excellent, it transpired that apparently some air receivers had not been subject to pressure tests. This probably reflected the fact that some lighthouses had limited local water supplies because of their remote locations high on cliff tops, etc. However, one of HSE's engineering inspectors observed that lighthouses usually also had oil stored in large tanks and suggested that such oil could be used instead of water as the fluid for hydraulic testing of the receivers. Because of a subsequent transfer to another HSE group in a different geographical area I don't know if the suggestion was put into practice and whether or not it caused any problems. However, from visits as a member of the public to lighthouses during recent years I learned that their foghorn systems became redundant after GPS systems became standard navigational tools on all types of seagoing vessels.