code: public static void assertHeaderContains(SipMessage sipMessage, String header, String value) {
      assertHeaderContains(null, sipMessage, header, value); // value is case
      // sensitive?
    }
docs: Asserts that the given SIP message contains at least one occurrence of the specified header and
  that at least one occurrence of this header contains the given value. The assertion fails if no
  occurrence of the header contains the value or if the header is not present in the mesage.
  
  @param sipMessage the SIP message.
  @param header the string identifying the header as specified in RFC-3261.
  @param value the string value within the header to look for. An exact string match is done
  against the entire contents of the header. The assertion will pass if any part of the
  header matches the value given.