add a sample

src/lib.rs

@@ -1,7 +1,20 @@
+#[allow(dead_code)]
+mod about_variables {
+    pub fn guess_this () -> i32 {
+        let one = 5;
+        let two = 7;
+        let three = 3;
+        let result = (one + two) / three;
+        result
+    }
+}
+
 #[cfg(test)]
 mod tests {
+    use super::about_variables::*;
+
     #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
+    fn test_complicated () {
+        assert_eq!(___, guess_this());
     }
 }