add missing lib

lib/ArduinoJson/test/JsonVariant/CMakeLists.txt

@@ -0,0 +1,19 @@
+# ArduinoJson - arduinojson.org
+# Copyright Benoit Blanchon 2014-2018
+# MIT License
+
+add_executable(JsonVariantTests 
+	as.cpp
+	compare.cpp
+	copy.cpp
+	is.cpp
+	or.cpp
+	printTo.cpp
+	set_get.cpp
+	subscript.cpp
+	success.cpp
+	undefined.cpp
+)
+
+target_link_libraries(JsonVariantTests catch)
+add_test(JsonVariant JsonVariantTests)