tests: use Signals from DummyClientFace

refs #2319

Change-Id: I688816fc58828a4f2d8fbad4936cc064816ab123
diff --git a/tests/unit/validator.cpp b/tests/unit/validator.cpp
index cda5e06..e51782b 100644
--- a/tests/unit/validator.cpp
+++ b/tests/unit/validator.cpp
@@ -59,7 +59,7 @@
     m_keyChain.addCertificate(*cert);
     NDNS_LOG_TRACE("add cert: " << cert->getName() << " to KeyChain");
 
-    m_face->onInterest += bind(&Fixture::respondInterest, this, _1);
+    m_face->onSendInterest.connect(bind(&Fixture::respondInterest, this, _1));
   }
 
   ~Fixture()