add_one fn

src/lib.rs

@@ -0,0 +1,19 @@
+#[no_mangle]
+pub extern "C" fn add_one(x: u32) -> u32 {
+    x + 1
+}
+
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}