Add PHPUnit test for wp_ob_end_flush_all function

tests/phpunit/tests/functions/wpObEndFlushAll.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * Tests for the wp_ob_end_flush_all function.
+ *
+ * @group functions
+ *
+ * @covers ::wp_ob_end_flush_all
+ */
+class Tests_Functions_wpObEndFlushAll extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 60177
+	 */
+	public function test_wp_ob_end_flush_all() {
+
+		ob_start();
+		echo 'output';
+
+		wp_ob_end_flush_all();
+		$this->assertEmpty( ob_get_contents(), 'All output buffers should be empty after wp_ob_end_flush_all()' );
+
+		// re-start ob as wp_ob_end_flush_all clears all the OB's and PHPunit has one open
+		ob_start();
+	}
+}