http://hg.openjdk.java.net/jdk6/jdk6/jdk/rev/d4f7664a6c3c added a regression test on Kerberos, but the test infrastructure was still not available in the repo. i.e. "6706974: Add krb5 test infrastructure" was not backported earlier.
Verified with OpenJDK 6 source bundle from http://download.java.net/openjdk/jdk6/. The test case /test/sun/security/krb5/auto/SpnegoReqFlags.java is removed from OpenJDK 6.