my $results;
my $test_data = [qw{foo bar baz}];
{
    no strict 'refs';
    local $^W; # suppres redefined warnings
    my $arrayref_called = 0;
    local *{'DBI::fetchrow_arrayref'} = sub {$arraref_called++; $test_data };
    $results = some_func($some_arg);
    is($arrayref_called, 1, '... and fetchrow_arrayref should be called only once');
}
ok($results, '... and some_func succeeded');
is_deeply($results, $test_data, '... and it should return the correct data');