draft: adding unit tests for the algorithm formulas

sn_networking/src/sybil.rs

@@ -152,3 +152,41 @@ fn common_prefix_length(lhs: &[u8], rhs: &[u8]) -> usize {
     }
     common_prefix_length
 }
+
+#[cfg(test)]
+mod tests {
+    use super::common_prefix_length;
+
+    use xor_name::XorName;
+
+    #[test]
+    fn test_common_prefix_length() {
+        // we use XorName utilities as it's easier to build test data with them
+        let mut rng = rand::thread_rng();
+        let mut lhs = XorName::random(&mut rng);
+        assert_eq!(common_prefix_length(&lhs, &lhs), 256);
+
+        let mut rhs = !lhs;
+        // let's first make sure lhs != rhs in every bit
+        assert_eq!(common_prefix_length(&lhs, &rhs), 0);
+
+        for i in 0..=255 {
+            lhs = lhs.with_bit(i, true);
+            rhs = rhs.with_bit(i, true);
+            assert_eq!(
+                i as usize + 1,
+                common_prefix_length(&lhs, &rhs),
+                "unexpected result from common_prefix_length fn"
+            );
+        }
+    }
+
+    #[test]
+    fn test_net_size_estimate() {
+        // Build a map with 256 random keys, one for each Kbucket
+        // with their corresponding K-closest peers to a random CID;
+        // e.g. in Kbucket #2 get the 20 closest peers to a random CID that shares 2 bits as a prefix.
+
+        todo!()
+    }
+}