How to use PHPUnit assert methods in a Codeception functional test?

\PHPUnit_Framework_Assert::assertSame()

Since Codeception 2.1 (not 2.0) you can use it like the other asserts with:

$I->assertSame($expected, $actual, $message);

But don't forget to enable the Asserts module in your config - e.g.:

class_name: UnitTester
modules:
    enabled: [ Asserts ]

Please note: You might need to change your configuration when upgrading to 2.1 - see upgrade instructions: http://codeception.com/06-19-2015/codeception-2.1-rc.html