Remove magic values as exit codes in test application (#777)

test/test.h

@@ -6,6 +6,23 @@
 #include <string.h>
 #include "wren.h"
 
+// Exit codes used by the wren binaries, following the BSD standard
+//
+// The interpreter was used with an incorrect number of arguments
+#define WREN_EX_USAGE 64
+
+// Compilation error
+#define WREN_EX_DATAERR 65
+
+// Runtime error
+#define WREN_EX_SOFTWARE 70
+
+// Cannot open input file
+#define WREN_EX_NOINPUT 66
+
+// I/O Error
+#define WREN_EX_IOERR 74
+
 // The maximum number of components in a path. We can't normalize a path that
 // contains more than this number of parts. The number here assumes a max path
 // length of 4096, which is common on Linux, and then assumes each component is
@@ -69,4 +86,4 @@ typedef struct
   WrenInterpretResult runFile(WrenVM* vm, const char* path);
   int handle_args(int argc, const char* argv[]);
 
-#endif //WREN_TEST_H
+#endif //WREN_TEST_H