cleanup path fn and add test coverage (#1201)

core/src/core/pmmr.rs

@@ -712,14 +712,11 @@ pub fn is_left_sibling(pos: u64) -> bool {
 /// The size (and therefore the set of peaks) of the MMR
 /// is defined by last_pos.
 pub fn path(pos: u64, last_pos: u64) -> Vec<u64> {
-	let mut path = vec![pos];
+	let mut path = vec![];
 	let mut current = pos;
-	while current + 1 <= last_pos {
+	while current <= last_pos {
+		path.push(current);
 		let (parent, _) = family(current);
-		if parent > last_pos {
-			break;
-		}
-		path.push(parent);
 		current = parent;
 	}
 	path

core/tests/pmmr.rs

@@ -97,6 +97,14 @@ fn various_families() {
 	assert_eq!(pmmr::family(1_000), (1_001, 997));
 }
 
+#[test]
+fn test_paths() {
+	assert_eq!(pmmr::path(1, 1), [1]);
+	assert_eq!(pmmr::path(1, 3), [1, 3]);
+	assert_eq!(pmmr::path(2, 3), [2, 3]);
+	assert_eq!(pmmr::path(4, 16), [4, 6, 7, 15]);
+}
+
 #[test]
 fn test_is_left_sibling() {
 	assert_eq!(pmmr::is_left_sibling(1), true);