diff --git a/tests/phpunit/includes/factory/class-wp-unittest-factory.php b/tests/phpunit/includes/factory/class-wp-unittest-factory.php
index 3b74092e62..4d0934bb9a 100644
--- a/tests/phpunit/includes/factory/class-wp-unittest-factory.php
+++ b/tests/phpunit/includes/factory/class-wp-unittest-factory.php
@@ -8,52 +8,72 @@
 class WP_UnitTest_Factory {
 
 	/**
+	 * Generates post fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Post
 	 */
 	public $post;
 
 	/**
+	 * Generates attachment fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Attachment
 	 */
 	public $attachment;
 
 	/**
+	 * Generates comment fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Comment
 	 */
 	public $comment;
 
 	/**
+	 * Generates user fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_User
 	 */
 	public $user;
 
 	/**
+	 * Generates taxonomy term fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Term
 	 */
 	public $term;
 
 	/**
+	 * Generates category fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Term
 	 */
 	public $category;
 
 	/**
+	 * Generates tag fixtures for use in tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Term
 	 */
 	public $tag;
 
 	/**
+	 * Generates bookmark (link) fixtures for use in tests.
+	 *
 	 * @since 4.6.0
 	 * @var WP_UnitTest_Factory_For_Bookmark
 	 */
 	public $bookmark;
 
 	/**
+	 * Generates blog (site) fixtures for use in Multisite tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Blog
 	 */
 	public $blog;
 
 	/**
+	 * Generates network fixtures for use in Multisite tests.
+	 *
 	 * @var WP_UnitTest_Factory_For_Network
 	 */
 	public $network;
diff --git a/tests/phpunit/includes/mock-mailer.php b/tests/phpunit/includes/mock-mailer.php
index d02d2efc69..ee04ce0627 100644
--- a/tests/phpunit/includes/mock-mailer.php
+++ b/tests/phpunit/includes/mock-mailer.php
@@ -76,7 +76,7 @@ class MockPHPMailer extends PHPMailer\PHPMailer\PHPMailer {
  *
  * @since 4.4.0
  *
- * @return object|bool
+ * @return MockPHPMailer|false
  */
 function tests_retrieve_phpmailer_instance() {
 	$mailer = false;
diff --git a/tests/phpunit/includes/utils.php b/tests/phpunit/includes/utils.php
index b178418de7..7a0de67377 100644
--- a/tests/phpunit/includes/utils.php
+++ b/tests/phpunit/includes/utils.php
@@ -2,10 +2,23 @@
 
 // Misc help functions and utilities.
 
+/**
+ * Returns a string of the required length containing random characters. Note that
+ * the maximum possible string length is 32.
+ *
+ * @param int $len Optional. The required length. Default 32.
+ * @return string The string.
+ */
 function rand_str( $len = 32 ) {
 	return substr( md5( uniqid( rand() ) ), 0, $len );
 }
 
+/**
+ * Returns a string of the required length containing random characters.
+ *
+ * @param int $len The required length.
+ * @return string The string.
+ */
 function rand_long_str( $length ) {
 	$chars  = 'abcdefghijklmnopqrstuvwxyz';
 	$string = '';
@@ -18,7 +31,12 @@ function rand_long_str( $length ) {
 	return $string;
 }
 
-// Strip leading and trailing whitespace from each line in the string.
+/**
+ * Strips leading and trailing whitespace from each line in the string.
+ *
+ * @param string $txt The text.
+ * @return string Text with line-leading and line-trailing whitespace stripped.
+ */
 function strip_ws( $txt ) {
 	$lines  = explode( "\n", $txt );
 	$result = array();
@@ -33,9 +51,11 @@ function strip_ws( $txt ) {
 
 /*
  * Helper class for testing code that involves actions and filters.
+ *
  * Typical use:
- * $ma = new MockAction();
- * add_action( 'foo', array( &$ma, 'action' ) );
+ *
+ *     $ma = new MockAction();
+ *     add_action( 'foo', array( &$ma, 'action' ) );
  */
 class MockAction {
 	public $events;
@@ -240,11 +260,31 @@ class TestXMLParser {
 	}
 }
 
+/**
+ * Converts an XML string into an array tree structure.
+ *
+ * The output of this function can be passed to xml_find() to find nodes by their path.
+ *
+ * @param string $in The XML string.
+ * @return array XML as an array.
+ */
 function xml_to_array( $in ) {
 	$p = new TestXMLParser( $in );
 	return $p->data;
 }
 
+/**
+ * Finds XML nodes by a given "path".
+ *
+ * Example usage:
+ *
+ *     $tree = xml_to_array( $rss );
+ *     $items = xml_find( $tree, 'rss', 'channel', 'item' );
+ *
+ * @param array     $tree     An array tree structure of XML, typically from xml_to_array().
+ * @param string ...$elements Names of XML nodes to create a "path" to find within the XML.
+ * @return array Array of matching XML node information.
+ */
 function xml_find( $tree, ...$elements ) {
 	$n   = count( $elements );
 	$out = array();