improve the robustness of ndncert library

Change-Id: Iaabc4d8f28ca27a7e7f501ebd122c5231ceb3ac0
diff --git a/tests/unit-tests/ca.conf.test3 b/tests/unit-tests/ca.conf.test3
new file mode 100644
index 0000000..f12eabb
--- /dev/null
+++ b/tests/unit-tests/ca.conf.test3
@@ -0,0 +1,10 @@
+{
+  "ca-prefix": "/ndn",
+  "issuing-freshness": "720",
+  "validity-period": "360",
+  "ca-info": "ndn testbed ca",
+  "supported-challenges":
+  [
+      { "type": "PINN" }
+  ]
+}
\ No newline at end of file