Using Google Ngram Viewer and the search terms the fruit are,the fruit is,the fruits are,and then chosing the first quote, taken from a recently published book by a native speaking author, we have
- The Woody Plant Seed Manual - Page 473
United States. Forest Service, F. T. Bonner, Robert P. Karrfalt - 2008 Found inside – Page 473
The fruits are juicy , 1- to 10 - seeded berries with enlarged , persistent calyxes at the base ( LHBH 1976 ).
- United States Plant Patents - Page 18 United States. Patent and Trademark Office - 2008
The size of the fruit is large or similar to the size of the fruit of Mutzu. The ratio of height ..
- The Encyclopedia of Fruit and Nuts - 2008 edited by Jules Janick, Robert E. Paull Found inside – Page 161 Very commonly, the fruit are covered with a waxy bloom.
The inescapable conclusion is that all are correct in context.
[20200924 - Example at 3. replaced by an example to include "fruit are"]