Add tests for and fix is_valid_position

src/bitwise.cpp

@@ -50,5 +50,5 @@ int get_file(int position){
 // it indicates that is it off the board.
 // ASSUMING position <= 128 but if it was that big that'd be weird.
 bool is_valid_position(int position){
-	return (position & 0x40);
+	return !(position & 0x40);
 }

tests/bitwise_tests.cpp

@@ -83,3 +83,9 @@ TEST_CASE("Test that bitwise operators return appropriate values. Move.from", "[
 	CHECK(get_castle_flag(MOVE_H1_TO_G1_AND_get_castle_flagLE) == 1);
 }
 
+TEST_CASE("Test that is_valid_position works properly", "[is_valid_position]"){
+	CHECK(is_valid_position(0));
+	CHECK(is_valid_position(63));
+	CHECK_FALSE(is_valid_position(-1));
+	CHECK_FALSE(is_valid_position(64));
+}