diff --git a/admin/tool/phpunit/index.php b/admin/tool/phpunit/index.php
index 489a910134b..774d4eec0c9 100644
--- a/admin/tool/phpunit/index.php
+++ b/admin/tool/phpunit/index.php
@@ -35,4 +35,4 @@ $info = file_get_contents("$CFG->libdir/phpunit/readme.md");
 echo markdown_to_html($info);
 
 echo $OUTPUT->box_end();
-echo $OUTPUT->footer();
\ No newline at end of file
+echo $OUTPUT->footer();
diff --git a/lib/phpunit/bootstrap.php b/lib/phpunit/bootstrap.php
index 8f4023597ce..f6ac22f4bb9 100644
--- a/lib/phpunit/bootstrap.php
+++ b/lib/phpunit/bootstrap.php
@@ -146,7 +146,7 @@ if (isset($CFG->prefix) and $CFG->prefix === $CFG->phpunit_prefix) {
     phpunit_bootstrap_error(131, '$CFG->prefix and $CFG->phpunit_prefix must not be identical, can not run tests!');
 }
 
-// override CFG settings if necessary nad throw away extra CFG settings
+// override CFG settings if necessary and throw away extra CFG settings
 $CFG->dataroot  = $CFG->phpunit_dataroot;
 $CFG->prefix    = $CFG->phpunit_prefix;
 $CFG->dbtype    = isset($CFG->phpunit_dbtype) ? $CFG->phpunit_dbtype : $CFG->dbtype;
diff --git a/lib/phpunit/bootstraplib.php b/lib/phpunit/bootstraplib.php
index 42964c68d59..82d6c28c2ac 100644
--- a/lib/phpunit/bootstraplib.php
+++ b/lib/phpunit/bootstraplib.php
@@ -63,7 +63,7 @@ function phpunit_bootstrap_error($errorcode, $text = '') {
             break;
     }
     if (defined('PHPUNIT_UTIL') and PHPUNIT_UTIL) {
-        // do not write to error stream because we need the error message in PHP exec from web ui
+        // do not write to error stream because we need the error message in PHP exec result from web ui
         echo($text."\n");
     } else {
         fwrite(STDERR, $text."\n");
@@ -103,4 +103,4 @@ function phpunit_boostrap_fix_file_permissions($file) {
     }
 
     return true;
-}
\ No newline at end of file
+}
diff --git a/lib/phpunit/generatorlib.php b/lib/phpunit/generatorlib.php
index 7f7b3ad9aa3..b0c809d4f13 100644
--- a/lib/phpunit/generatorlib.php
+++ b/lib/phpunit/generatorlib.php
@@ -87,6 +87,11 @@ EOD;
         }
     }
 
+    /**
+     * Return generator for given plugin
+     * @param string $component
+     * @return mixed plugin data generator
+     */
     public function get_plugin_generator($component) {
         list($type, $plugin) = normalize_component($component);
 
@@ -539,7 +544,7 @@ abstract class phpunit_module_generator {
         context_module::instance($cm->id);
 
         return $cm;
-  }
+    }
 
     /**
      * Create a test module
diff --git a/lib/phpunit/lib.php b/lib/phpunit/lib.php
index bbe0e7547dc..fa99d49719d 100644
--- a/lib/phpunit/lib.php
+++ b/lib/phpunit/lib.php
@@ -46,7 +46,7 @@ class phpunit_util {
     protected static $tablestructure = null;
 
     /**
-     * @var array An array of globals cloned from CFG
+     * @var array An array of original globals, restored after each test
      */
     protected static $globals = array();
 
@@ -60,13 +60,17 @@ class phpunit_util {
      */
     protected static $generator = null;
 
+    /**
+     * @var resource used for prevention of parallel test execution
+     */
     protected static $lockhandle = null;
 
     /**
-     * Prevent parallel test execution - this can not work in Moodle because we modify DB and dataroot.
+     * Prevent parallel test execution - this can not work in Moodle because we modify database and dataroot.
      *
      * Note: do not call manually!
      *
+     * @internal
      * @static
      * @return void
      */
@@ -99,6 +103,7 @@ class phpunit_util {
 
     /**
      * Note: do not call manually!
+     * @internal
      * @static
      * @return void
      */
@@ -383,7 +388,7 @@ class phpunit_util {
     }
 
     /**
-     * Purge dataroot
+     * Purge dataroot directory
      * @static
      * @return void
      */
@@ -413,9 +418,9 @@ class phpunit_util {
      *
      * Note: this is relatively slow (cca 2 seconds for pg and 7 for mysql) - please use with care!
      *
+     * @static
      * @param bool $logchanges log changes in global state and database in error log
      * @return void
-     * @static
      */
     public static function reset_all_data($logchanges = false) {
         global $DB, $CFG, $USER, $SITE, $COURSE, $PAGE, $OUTPUT, $SESSION;
@@ -462,13 +467,13 @@ class phpunit_util {
             }
         }
 
-        // restore original config
+        // restore original globals
         $_SERVER = self::get_global_backup('_SERVER');
         $CFG = self::get_global_backup('CFG');
         $SITE = self::get_global_backup('SITE');
         $COURSE = $SITE;
 
-        // recreate globals
+        // reinitialise following globals
         $OUTPUT = new bootstrap_renderer();
         $PAGE = new moodle_page();
         $FULLME = null;
@@ -477,7 +482,7 @@ class phpunit_util {
         $SESSION = new stdClass();
         $_SESSION['SESSION'] =& $SESSION;
 
-        // set fresh new user
+        // set fresh new not-logged-in user
         $user = new stdClass();
         $user->id = 0;
         $user->mnethostid = $CFG->mnet_localhost_id;
@@ -489,10 +494,10 @@ class phpunit_util {
         events_get_handlers('reset');
         //TODO: add more resets here and probably refactor them to new core function
 
-        // purge dataroot
+        // purge dataroot directory
         self::reset_dataroot();
 
-        // restore original config once more in case resetting of caches changes CFG
+        // restore original config once more in case resetting of caches changed CFG
         $CFG = self::get_global_backup('CFG');
 
         // inform data generator
@@ -503,7 +508,7 @@ class phpunit_util {
 
         // verify db writes just in case something goes wrong in reset
         if (self::$lastdbwrites != $DB->perf_get_writes()) {
-            error_log('Unexpected DB writes in reset_all_data.');
+            error_log('Unexpected DB writes in phpunit_util::reset_all_data()');
             self::$lastdbwrites = $DB->perf_get_writes();
         }
 
@@ -515,7 +520,9 @@ class phpunit_util {
 
     /**
      * Called during bootstrap only!
+     * @internal
      * @static
+     * @return void
      */
     public static function bootstrap_init() {
         global $CFG, $SITE, $DB;
@@ -732,7 +739,7 @@ class phpunit_util {
     }
 
     /**
-     * Calculate unique version hash for all available plugins and core.
+     * Calculate unique version hash for all plugins and core.
      * @static
      * @return string sha1 hash
      */
@@ -777,7 +784,7 @@ class phpunit_util {
     }
 
     /**
-     * Builds dirroot/phpunit.xml and dataroot/phpunit/webrunner.xml file using defaults from /phpunit.xml.dist
+     * Builds dirroot/phpunit.xml and dataroot/phpunit/webrunner.xml files using defaults from /phpunit.xml.dist
      * @static
      * @return bool true means main config file created, false means only dataroot file created
      */
@@ -852,7 +859,7 @@ class UnitTestCase extends PHPUnit_Framework_TestCase {
      * @return void
      */
     public function expectException($expected, $message = '') {
-        // use phpdocs: @expectedException ExceptionClassName
+        // alternatively use phpdocs: @expectedException ExceptionClassName
         if (!$expected) {
             return;
         }
@@ -976,7 +983,7 @@ class basic_testcase extends PHPUnit_Framework_TestCase {
     /**
      * Constructs a test case with the given name.
      *
-     * Note: use setUp() or setUpBeforeClass() in custom test cases.
+     * Note: use setUp() or setUpBeforeClass() in your test cases.
      *
      * @param string $name
      * @param array  $data
@@ -1033,7 +1040,7 @@ class advanced_testcase extends PHPUnit_Framework_TestCase {
     /**
      * Constructs a test case with the given name.
      *
-     * Note: use setUp() or setUpBeforeClass() in custom test cases.
+     * Note: use setUp() or setUpBeforeClass() in your test cases.
      *
      * @param string $name
      * @param array  $data
@@ -1119,6 +1126,9 @@ class advanced_testcase extends PHPUnit_Framework_TestCase {
      * Call this method from test if you want to make sure that
      * the resetting of database is done the slow way without transaction
      * rollback.
+     *
+     * This is useful especially when testing stuff that is not compatible with transactions.
+     *
      * @return void
      */
     public function preventResetByRollback() {