                           traverse(node);
                            }
                        }
                    };

                    let tree = {
                        test: test_nodes,
                        overlaps: new Map(), // map: span_id -> OVERLAP
                        children: new Map(), // map: index -> struct
                    };

                    gather_overlaps(tree, file, coverage_nodes, from, to);

                    traverse(tree);

                    return out;
    