Add proof of private key challenge

Change-Id: Ic48b65c550603656c962e3c251f4dac1759cb4a1
diff --git a/tests/unit-tests/challenge-credential.t.cpp b/tests/unit-tests/challenge-credential.t.cpp
index 3472687..7b101d7 100644
--- a/tests/unit-tests/challenge-credential.t.cpp
+++ b/tests/unit-tests/challenge-credential.t.cpp
@@ -91,7 +91,7 @@
   params.push_back(makeStringBlock(tlv_selected_challenge, "Credential"));
   params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_CREDENTIAL_CERT));
   params.push_back(makeStringBlock(tlv_parameter_value, credentialStr));
-  params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_CREDENTIAL_SELF));
+  params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_PROOF_OF_PRIVATE_KEY));
   params.push_back(makeStringBlock(tlv_parameter_value, selfSignedStr));
   params.encode();