update header files in tests

Change-Id: Ibfffb9367349f58eeb193350bad34fdfccd8c553
diff --git a/tests/unit-tests/challenge-credential.t.cpp b/tests/unit-tests/challenge-credential.t.cpp
index 9072fa0..566ffd8 100644
--- a/tests/unit-tests/challenge-credential.t.cpp
+++ b/tests/unit-tests/challenge-credential.t.cpp
@@ -19,7 +19,7 @@
  */
 
 #include "challenge-module/challenge-credential.hpp"
-#include "identity-management-fixture.hpp"
+#include "test-common.hpp"
 #include <ndn-cxx/security/signing-helpers.hpp>
 #include <ndn-cxx/util/io.hpp>
 
@@ -101,6 +101,6 @@
 
 BOOST_AUTO_TEST_SUITE_END()
 
-} // namespace tests
-} // namespace ndncert
-} // namespace ndn
+}  // namespace tests
+}  // namespace ndncert
+}  // namespace ndn