use warnings;
use strict;

my @tests = ("this     is+   +test",
             "this+test",
             "morepluses+++++++test");

for (@tests)
{
   s/\++/ /g; #multiple+ to single space (see note)
   print "$_\n";

}
__END__
this     is     test
this test
morepluses test

or could use this regex to also compress spaces:

s/[\s\+]+/ /g; #multiple spaces or + to single space
this is test
this test
morepluses test

##</code><code>##

use warnings;
use strict;

my @tests = ("this     is+   +test",
             "this+test",
             "morepluses+++++++test");

for (@tests)
{
   tr /+/ /;  #lower overhead than the regex engine
   print "$_\n";

}
__END__
this     is     test
this test
morepluses       test