MDL-60342 test: Reset user agent after tests

- Add a test that proves this useragent is not being reset after a test
- Reset user agent

lib/phpunit/classes/util.php

@@ -277,6 +277,9 @@ public static function reset_all_data($detectchanges = false) {
         // Reset the log manager cache.
         get_log_manager(true);
 
+        // Reset user agent.
+        core_useragent::instance(true, null);
+
         // verify db writes just in case something goes wrong in reset
         if (self::$lastdbwrites != $DB->perf_get_writes()) {
             error_log('Unexpected DB writes in phpunit_util::reset_all_data()');

lib/phpunit/tests/advanced_test.php

@@ -662,4 +662,23 @@ public function test_locale_reset() {
             $this->assertSame('en_AU.UTF-8', setlocale(LC_TIME, 0));
         }
     }
+
+    /**
+     * This test sets a user agent and makes sure that it is cleared when the test is reset.
+     */
+    public function test_it_resets_useragent_after_test() {
+        $this->resetAfterTest();
+        $fakeagent = 'New user agent set.';
+
+        // Sanity check: it should not be set when test begins.
+        self::assertFalse(core_useragent::get_user_agent_string(), 'It should not be set at first.');
+
+        // Set a fake useragent and check it was set properly.
+        core_useragent::instance(true, $fakeagent);
+        self::assertSame($fakeagent, core_useragent::get_user_agent_string(), 'It should be the forced agent.');
+
+        // Reset test data and ansure the useragent was cleaned.
+        self::resetAllData(false);
+        self::assertFalse(core_useragent::get_user_agent_string(), 'It should not be set again, data was reset.');
+    }
 }