Tests: added generic tests for $arg_ variables.

http_variables.t

diff --git a/http_variables.t b/http_variables.t
index 2bc98b5..7ea6325 100644
--- a/http_variables.t
+++ b/http_variables.t
@@ -22,7 +22,7 @@
 select STDERR; $| = 1;
 select STDOUT; $| = 1;
 
-my $t = Test::Nginx->new()->has(qw/http rewrite proxy/)->plan(6);
+my $t = Test::Nginx->new()->has(qw/http rewrite proxy/)->plan(7);
 
 $t->write_file_expand('nginx.conf', <<'EOF');
 
@@ -48,6 +48,10 @@
             return 200 OK;
         }
 
+        location /arg {
+            return 200 $arg_l:$arg_;
+        }
+
         location /set {
             add_header Cache-Control max-age=3600;
             add_header Cache-Control private;
@@ -78,6 +82,14 @@
 http_get('/../bad_uri');
 http_get('/redefine');
 
+TODO: {
+todo_skip 'overflow', 1 unless $ENV{TEST_NGINX_UNSAFE}
+	or $t->has_version('1.19.0');
+
+like(http_get('/arg?l=42'), qr/42:$/, 'arg');
+
+}
+
 # $limit_rate is a special variable that has its own set_handler / get_handler
 
 like(http_get('/limit_rate?l=40k'), qr/X-Rate: 40960/, 'limit_rate handlers');