Index: tests/phpunit/tests/query/orderby.php
===================================================================
--- tests/phpunit/tests/query/orderby.php	(nonexistent)
+++ tests/phpunit/tests/query/orderby.php	(working copy)
@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * Tests for query result ordering, specifically indeterminate ordering.
+ *
+ * @group query
+ */
+class Tests_Query_Orderby extends WP_UnitTestCase {
+	function test_order_by_comment_count_does_not_cause_duplication_when_paginating() {
+		global $wpdb;
+
+		$posts = self::factory()->post->create_many( 5 );
+
+		$wpdb->update(
+			$wpdb->posts,
+			array(
+				'comment_count' => 50,
+			),
+			array(
+				'ID' => $posts[2],
+			)
+		);
+		$wpdb->update(
+			$wpdb->posts,
+			array(
+				'comment_count' => 100,
+			),
+			array(
+				'ID' => $posts[4],
+			)
+		);
+		$args = array(
+			'posts_per_page' => 1,
+			'paged'          => 1,
+			'orderby'        => 'comment_count',
+			'order'          => 'desc',
+		);
+
+		$query    = new WP_Query( $args );
+		$actual   = array();
+		$expected = array(
+			$posts[4], // 100 comments
+			$posts[2], // 50 comments
+			$posts[3], // 0 comments
+			$posts[1], // 0 comments
+			$posts[0], // 0 comments
+		);
+
+		while ( $query->have_posts() ) {
+			$actual = array_merge( $actual, wp_list_pluck( $query->posts, 'ID' ) );
+			$args['paged']++;
+			$query = new WP_Query( $args );
+		}
+
+		$this->assertSame( $expected, $actual );
+	}
+}

Property changes on: tests/phpunit/tests/query/orderby.php
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Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property