Verify that '/' is parent of everything

Bug could occur when run with '/' as it wasn't considered the parent of
'/usr' due to having the same number of '/'s in the name

src/utils/mod.rs

@@ -37,7 +37,7 @@ impl PartialEq for Node {
 }
 
 pub fn is_a_parent_of(parent: &str, child: &str) -> bool {
-    child.starts_with(parent) && child.chars().nth(parent.chars().count()) == Some('/')
+    (child.starts_with(parent) && child.chars().nth(parent.chars().count()) == Some('/')) || parent == "/"
 }
 
 pub fn simplify_dir_names(filenames: Vec<&str>) -> HashSet<String> {
@@ -232,4 +232,18 @@ mod tests {
         correct.insert("src_v2".to_string());
         assert_eq!(simplify_dir_names(vec!["src/", "src_v2"]), correct);
     }
+
+    #[test]
+    fn test_is_a_parent_of() {
+        assert!(is_a_parent_of("/usr", "/usr/andy"));
+        assert!(is_a_parent_of("/usr", "/usr/andy/i/am/descendant"));
+        assert!(!is_a_parent_of("/usr/andy", "/usr"));
+        assert!(!is_a_parent_of("/usr/andy", "/usr/sibling"));
+    }
+
+    #[test]
+    fn test_is_a_parent_of_root() {
+        assert!(is_a_parent_of("/", "/usr/andy"));
+        assert!(is_a_parent_of("/", "/usr"));
+    }
 }