Migrate JavaTokenParsers tests to JUnit.

The unicode strings has been escaped using

  native2ascii -encoding utf8 a.txt b.txt

command.
Reduce code duplication in PackratParsersTest

Extract common code that parses strings and extracts results
into helper methods.

In test1 and test2 I named the helper method `check` because it checks
if expression-evaluating parser calculates the correct result.

In test3, we are interested in parsing result (Success or Failure) thus
helper methods are named `assertSuccess` and `assertFailure`.