Using Google Ngram Viewer and the search terms [the fruit are,the fruit is,the fruits are][1], and then choosing the first quote, taken from a recently published book by a native speaking author, we have


1. **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 )*. 

2. **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 ..*

3. **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"]*


  [1]: https://books.google.com/ngrams/graph?smoothing=3&corpus=26&year_end=2019&year_start=1800&content=the%20fruit%20are%2Cthe%20fruit%20is%2Cthe%20fruits%20are&direct_url=t1%3B%2Cthe%20fruit%20are%3B%2Cc0%3B.t1%3B%2Cthe%20fruit%20is%3B%2Cc0%3B.t1%3B%2Cthe%20fruits%20are%3B%2Cc0#t1%3B%2Cthe%20fruit%20are%3B%2Cc0%3B.t1%3B%2Cthe%20fruit%20is%3B%2Cc0%3B.t1%3B%2Cthe%20fruits%20are%3B%2Cc0