--- /dev/null
+use warnings;
+use strict;
+
+use RT::Test nodata => 1, tests => undef;
+use RT::I18N;
+use Test::Warn;
+
+diag "normal mime encoding conversion: utf8 => iso-8859-1";
+{
+ my $mime = MIME::Entity->build(
+ Type => 'text/plain; charset=utf-8',
+ Data => ['À中文'],
+ );
+
+ warning_like {
+ RT::I18N::SetMIMEEntityToEncoding( $mime, 'iso-8859-1', );
+ }
+ [ qr/does not map to iso-8859-1/ ], 'got one "not map" error';
+ is( $mime->stringify_body, 'À中文', 'body is not changed' );
+ is( $mime->head->mime_attr('Content-Type'), 'application/octet-stream' );
+}
+
+diag "mime encoding conversion: utf8 => iso-8859-1";
+{
+ my $mime = MIME::Entity->build(
+ Type => 'text/plain; charset=utf-8',
+ Data => ['À中文'],
+ );
+ is( $mime->stringify_body, 'À中文', 'body is not changed' );
+}
+
+done_testing;