Add working unit tests

test/emul/Arduino.h

@@ -0,0 +1,18 @@
+#ifndef ARDUINO_H
+#define ARDUINO_H
+
+#include <stdint.h>
+
+#include "esp-hal-gpio.h"
+
+void pinMode(uint8_t pin, uint8_t mode);
+void digitalWrite(uint8_t pin, uint8_t val);
+int digitalRead(uint8_t pin);
+
+// Can be previously declared as a macro in stupid eModbus
+#undef millis
+unsigned long millis();
+
+#define max(a, b) std::max(a, b)
+
+#endif