Add more tests verifying that the H1-H6 elements close opened heading…

… elements.

tests/phpunit/tests/html-api/wpHtmlProcessorSemanticRules.php

@@ -135,10 +135,23 @@ public function test_in_body_button_with_button_in_scope_as_ancestor() {
 	 * @param string $tag_name Name of H1 - H6 element under test.
 	 */
 	public function test_heading_element_closes_open_p_tag( $tag_name ) {
-		$p = WP_HTML_Processor::create_fragment( "<p>Open<{$tag_name}>Closed P</{$tag_name}></p>" );
+		$processor = WP_HTML_Processor::create_fragment(
+			"<p>Open<{$tag_name}>Closed P</{$tag_name}><img></p>"
+		);
+
+		$processor->next_tag( $tag_name );
+		$this->assertSame(
+			array( 'HTML', 'BODY', $tag_name ),
+			$processor->get_breadcrumbs(),
+			"Expected {$tag_name} to be a direct child of the BODY, having closed the open P element."
+		);
 
-		$p->next_tag( $tag_name );
-		$this->assertSame( array( 'HTML', 'BODY', $tag_name ), $p->get_breadcrumbs() );
+		$processor->next_tag( 'IMG' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'IMG' ),
+			$processor->get_breadcrumbs(),
+			'Expected IMG to be a direct child of BODY, having closed the open P element.'
+		);
 	}
 
 	/**
@@ -157,6 +170,65 @@ public function data_heading_elements() {
 		);
 	}
 
+	/**
+	 * Verifies that H1 through H6 elements close an open H1 through H6 element.
+	 *
+	 * @dataProvider data_heading_combinations
+	 *
+	 * @param string $first_heading  H1 - H6 element appearing (unclosed) before the second.
+	 * @param string $second_heading H1 - H6 element appearing after the first.
+	 */
+	public function test_heading_element_closes_other_heading_elements( $first_heading, $second_heading ) {
+		$processor = WP_HTML_Processor::create_fragment(
+			"<div><{$first_heading} first> then <{$second_heading} second> and end </{$second_heading}><img></{$first_heading}></div>"
+		);
+
+		while ( $processor->next_tag() && null === $processor->get_attribute( 'second' ) ) {
+			continue;
+		}
+
+		$this->assertTrue(
+			$processor->get_attribute( 'second' ),
+			"Failed to find expected {$second_heading} tag."
+		);
+
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'DIV', $second_heading ),
+			$processor->get_breadcrumbs(),
+			"Expected {$second_heading} to be a direct child of the DIV, having closed the open {$first_heading} element."
+		);
+
+		$processor->next_tag( 'IMG' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'DIV', 'IMG' ),
+			$processor->get_breadcrumbs(),
+			"Expected IMG to be a direct child of DIV, having closed the open {$first_heading} element."
+		);
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_heading_combinations() {
+		$headings = array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' );
+
+		$combinations = array();
+
+		// Create all unique pairs of H1 - H6 elements.
+		for ( $first = 0; $first < count( $headings ); $first++ ) {
+			for ( $second = $first; $second < count( $headings ); $second++ ) {
+				$first_tag  = $headings[ $first ];
+				$second_tag = $headings[ $second ];
+
+				$combinations[ "{$first_tag} then {$second_tag}" ] = array( $first_tag, $second_tag );
+			}
+		}
+
+		return $combinations;
+	}
+
 	/**
 	 * Verifies that when "in body" and encountering "any other end tag"
 	 * that the HTML processor ignores the end tag if there's a special