JSON instruction serialization fix.

unit_tests/engine/json_factory.cpp

@@ -0,0 +1,16 @@
+#include "engine/api/json_factory.hpp"
+
+#include <boost/test/test_case_template.hpp>
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_SUITE(json_factory)
+
+BOOST_AUTO_TEST_CASE(instructionTypeToString_test_size)
+{
+    using namespace osrm::engine::api::json::detail;
+    using namespace osrm::extractor::guidance;
+
+    BOOST_CHECK_EQUAL(instructionTypeToString(TurnType::Sliproad), "invalid");
+}
+
+BOOST_AUTO_TEST_SUITE_END()