N. Korea is helping Iran prepare for a nuke test?

The Telegraph is usually pretty good, so I believe they're reporting what they've been told, however, I question the veracity and motivation of what they're being told. (Single sourced?)

North Korea is helping Iran to prepare an underground nuclear test similar to the one Pyongyang carried out last year.....

A senior European defence official told The Daily Telegraph that North Korea had invited a team of Iranian nuclear scientists to study the results of last October's underground test to assist Teheran's preparations to conduct its own — possibly by the end of this year.

Related: The USS Stennis, the second carrier battlegroup heading to the Gulf, is expected to arrive in late February.