Is mandatory in Germany for any sort of business as being stipulated by mandatory "accident prevention and insurance association" or however you might call this type of social security in your country.
Portable devices are covered by VDE 0701 with a flexible schedule, the complete fixed installation is to be checked in 4 years schedule.
As far as I know in Austria frequent testing is mandatory too, though I absolutely don't know if this applies to all commercial settings or only certain fields. It's most certainly neglected frequently. The office building I'm sitting in right now (electrical planning office) was built in 1998 and the first check was done 2 weeks ago.
As Wolfgang mentioned in Germany the so-called Berufsgenossenschaft requests the testing. On (especially larger) constructions ites there are also checks I think. This is only confirmed by one story I heard though... An Italian plumbing company arrived on site with only dangling cords on their tools... not a single plug. They just too matches and stuffed the bare wires into the socket holes... they didn't want to carry around adaptors for their cords working in different countries.