Fixes to unit tests to work on native platform

test/test_crc/test_crc.cpp

@@ -2,6 +2,14 @@
 #include <Arduino.h>
 #include "PacketCRC.h"
 
+void setUp()
+{
+}
+
+void tearDown()
+{
+}
+
 void run_calculate_test(const uint8_t *packet_data, const uint16_t expected_checksum)
 {
   PacketCRC packetCRC;
@@ -82,4 +90,9 @@ void setup()
 
   runUnityTests();
 }
-void loop() {}
+void loop() {}
+
+int main(void)
+{
+  return runUnityTests();
+}