diff --git a/tests/phpunit/tests/functions/_cleanup_header_comment.php b/tests/phpunit/tests/functions/_cleanup_header_comment.php
new file mode 100644
index 0000000000..0f1ceed3b0
--- /dev/null
+++ b/tests/phpunit/tests/functions/_cleanup_header_comment.php
@@ -0,0 +1,121 @@
+<?php
+/*
+ * Test _cleanup_header_comment().
+ *
+ * @group functions.php
+ * @ticket 8497
+ * @ticket 38101
+ */
+class Tests_Cleanup_Header_Comment extends WP_UnitTestCase {
+	/**
+	 * Test cleanup header of header comment.
+	 *
+	 * @covers _cleanup_header_comment
+	 * @dataProvider data_cleanup_header_comment
+	 *
+	 * @param string $test_string
+	 * @param string $expected
+	 */
+	public function test_cleanup_header_comment( $test_string, $expected ) {
+		$this->assertEquals( $expected, _cleanup_header_comment( $test_string ) );
+	}
+
+	/**
+	 * Data provider for test_cleanup_header_comment.
+	 *
+	 * @return array[] Test parameters {
+	 *     @type string $test_string Test string.
+	 *     @type string $expected    Expected return value.
+	 * }
+	 */
+	public function data_cleanup_header_comment() {
+		return array(
+			// Set 0: A string.
+			array(
+				'ffffffffffffff',
+				'ffffffffffffff',
+			),
+			// Set 1: Trim a string.
+			array(
+				'	ffffffffffffff ',
+				'ffffffffffffff',
+			),
+			// Set 2: Trim a full comment string.
+			array(
+				'<?php
+/*
+Plugin Name: Health Check
+Plugin URI: https://wordpress.org/plugins/health-check/
+Description: Checks the health of your WordPress install
+Version: 0.1.0
+Author: The Health Check Team
+Author URI: http://health-check-team.example.com
+Text Domain: health-check
+Domain Path: /languages
+*/
+',
+				'<?php
+/*
+Plugin Name: Health Check
+Plugin URI: https://wordpress.org/plugins/health-check/
+Description: Checks the health of your WordPress install
+Version: 0.1.0
+Author: The Health Check Team
+Author URI: http://health-check-team.example.com
+Text Domain: health-check
+Domain Path: /languages',
+			),
+			// Set 3: Trim HTML following comment.
+			array(
+				'<?php
+/*
+Plugin Name: Health Check
+Plugin URI: https://wordpress.org/plugins/health-check/
+Description: Checks the health of your WordPress install
+Version: 0.1.0
+Author: The Health Check Team
+Author URI: http://health-check-team.example.com
+Text Domain: health-check
+Domain Path: /languages
+*/ ?>
+dddlddfs
+',
+				'<?php
+/*
+Plugin Name: Health Check
+Plugin URI: https://wordpress.org/plugins/health-check/
+Description: Checks the health of your WordPress install
+Version: 0.1.0
+Author: The Health Check Team
+Author URI: http://health-check-team.example.com
+Text Domain: health-check
+Domain Path: /languages
+dddlddfs',
+			),
+			// Set 4: Trim a docblock style comment.
+			array(
+				'<?php
+/**
+ * Plugin Name: Health Check
+ * Plugin URI: https://wordpress.org/plugins/health-check/
+ * Description: Checks the health of your WordPress install
+ * Version: 0.1.0
+ * Author: The Health Check Team
+ * Author URI: http://health-check-team.example.com
+ * Text Domain: health-check
+ * Domain Path: /languages
+ */',
+				'<?php
+/**
+ * Plugin Name: Health Check
+ * Plugin URI: https://wordpress.org/plugins/health-check/
+ * Description: Checks the health of your WordPress install
+ * Version: 0.1.0
+ * Author: The Health Check Team
+ * Author URI: http://health-check-team.example.com
+ * Text Domain: health-check
+ * Domain Path: /languages',
+			),
+		);
+	}
+}