My parents have two of those plants in their backyard. They forgot what it is. It produces fruits or vegetables. The leafs goes from green to almost black on the outside. The flowers are purple.
They would like to know what it is exactly.
I don't really know for sure, but the closest thing I've found appearance-wise is poroporo, AKA the kangaroo apple (Solanum aviculare, or Solanum laciniatum). There may be some subtle differences in appearance, though. It may also be the more poisonous large-flowered kangaroo apple (Solanum laciniatum Aiton).
The regular kangaroo apple is edible only when dark orange.