Detect adding new .result files

Part of #23

checkpatch.pl

@@ -2140,6 +2140,7 @@ sub process {
 
 	my %commit_log_tags = ();
 	my $has_changelog = 0;
+	my $has_diff_file = 0;
 	my $has_doc = 0;
 	my $has_test = 0;
 	my $is_test = 0;
@@ -2731,6 +2732,9 @@ sub process {
 		if ($realfile =~ /^(?:static-build\/)?test\/.*\//) {
 			$has_test = 1;
 		}
+		if ($realfile =~ /\.result$/) {
+			$has_diff_file = 1;
+		}
 
 # check for repeated words separated by a single space
 # avoid false positive from list command eg, '-rw-r--r-- 1 root root'
@@ -5158,6 +5162,10 @@ sub process {
 			ERROR("NO_TEST",
 			      "Please add test or NO_TEST=<reason> tag\n");
 		}
+		if ($has_test && $has_diff_file) {
+			ERROR("DIFF_FILE",
+			      "Please avoid tests with .result files\n");
+		}
 	}
 
 	print report_dump();