Some countries require similar driving skills and have similar licensing systems to New Zealand's. Depending on the country you have come from and the class of licence you are converting, you may not have to sit theory and/or practical tests. Other countries may have driver licensing systems that are very different from New Zealand's. People from these countries do have to sit both theory and practical tests.

Theory test?
You do not have to sit the theory test if:

you have a licence from Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, South Africa, Spain, Sweden, Switzerland, the United Kingdom or the United States of America, and
your licence is current (or has expired less than 12 months), and
you are converting a car or a motorcycle licence. You do have to sit a theory test if:

you have a licence from a country not listed above; or
you are converting a heavy vehicle licence from any country.
Practical test
You do not have to sit the practical test if:

you have a licence from Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, South Africa, Spain, Sweden, Switzerland, the United Kingdom or the United States of America, and
your licence is current (or has expired less than 12 months), and
you have held that licence for more than two years.
You do have to sit the practical test if:

you have a licence from a country not listed above, or
you are converting a heavy vehicle licence from any country, or
you have a licence from a country which is listed above but you have held that licence for less than two years.

bear in mind there is an on the spot fine if Police stop you driving and you have no license with you - there were some random checks a couple of Saturdays ago on the local back streets up here - you have been warned