Index: tests/phpunit/tests/formatting/WPSpecialchars.php
===================================================================
--- tests/phpunit/tests/formatting/WPSpecialchars.php	(revision 32685)
+++ tests/phpunit/tests/formatting/WPSpecialchars.php	(working copy)
@@ -39,4 +39,66 @@
 		$this->assertEquals( '"'hello!'"', _wp_specialchars($source, true) );
 		$this->assertEquals( $source, _wp_specialchars($source) );
 	}
+
+	/**
+	 * Check some of the double-encoding features for entity references.
+	 *
+	 * @ticket 17780
+	 * @dataProvider data_double_encoding
+	 */
+	function test_double_encoding( $input, $output ) {
+		return $this->assertEquals( $output, _wp_specialchars( $input, ENT_NOQUOTES, false, true ) );
+	}
+
+	function data_double_encoding() {
+		return array(
+			array(
+				'This & that, this & that, — " " Ú   " " " " " $ ×',
+				'This & that, this & that, — " " Ú   " " " " " $ ×',
+			),
+			array(
+				'&& && && &;',
+				'&& && && &;',
+			),
+			array(
+				'&garbage; &***; &aaaa; &0000; &####; &;;',
+				'&garbage; &***; &aaaa; &0000; &####; &;;',
+			),
+			array(
+				'& " —',
+				'& " —',
+			),
+		);
+	}
+
+	/**
+	 * Check some of the double-encoding features for entity references.
+	 *
+	 * @ticket 17780
+	 * @dataProvider data_no_double_encoding
+	 */
+	function test_no_double_encoding( $input, $output ) {
+		return $this->assertEquals( $output, _wp_specialchars( $input, ENT_NOQUOTES, false, false ) );
+	}
+
+	function data_no_double_encoding() {
+		return array(
+			array(
+				'This & that, this & that, — " " Ú   " " " " " $ ×',
+				'This & that, this & that, — " " Ú   " " " " " $ ×',
+			),
+			array(
+				'&& && && &;',
+				'&& && && &;',
+			),
+			array(
+				'&garbage; &***; &aaaa; &0000; &####; &;;',
+				'&garbage; &***; &aaaa; &0000; &####; &;;',
+			),
+			array(
+				'& " —',
+				'& " —',
+			),
+		);
+	}
 }