$languageInterface is a misleading variable name in TokenReplaceUnitTestBase

Looking at Drupal\node\Tests\NodeTokenReplaceTest from the perspective of #2226533: Changes to the Language class due to the LanguageInterface (followup)

This has highlighted a variable with an unfortunate variable name...

Consider this snippet of code from NodeTokenReplaceTest::testNodeTokenReplacement()

    foreach ($tests as $input => $expected) {
      $output = $this->tokenService->replace($input, array('node' => $node), array('langcode' => $this->languageInterface->id, 'sanitize' => FALSE));
      $this->assertEqual($output, $expected, format_string('Unsanitized node token %token replaced.', array('%token' => $input)));
    }

$this->languageInterface->id attempts to dynamically pull a property from a variable designated as an interface.
( Only constants can reasonably be accessed from an interface )

Other issue in the queue are trying to change this to ->id to ->getId()
see #2226533: Changes to the Language class due to the LanguageInterface (followup)
but that patch is already to unwieldy for this side issue.

I will post a patch shortly