diff --git a/test/rank/feasible-tree-test.js b/test/rank/feasible-tree-test.js
index 53f2f8c9..72f3e1a2 100644
--- a/test/rank/feasible-tree-test.js
+++ b/test/rank/feasible-tree-test.js
@@ -1,21 +1,21 @@
-var expect = require("../chai").expect;
-var Graph = require("@dagrejs/graphlib").Graph;
-var feasibleTree = require("../../lib/rank/feasible-tree");
+let expect = require("../chai").expect;
+let Graph = require("@dagrejs/graphlib").Graph;
+let feasibleTree = require("../../lib/rank/feasible-tree");
 
 describe("feasibleTree", () => {
   it("creates a tree for a trivial input graph", () => {
-    var g = new Graph()
+    let g = new Graph()
       .setNode("a", { rank: 0 })
       .setNode("b", { rank: 1 })
       .setEdge("a", "b", { minlen: 1 });
 
-    var tree = feasibleTree(g);
+    let tree = feasibleTree(g);
     expect(g.node("b").rank).to.equal(g.node("a").rank + 1);
     expect(tree.neighbors("a")).to.eql(["b"]);
   });
 
   it("correctly shortens slack by pulling a node up", () => {
-    var g = new Graph()
+    let g = new Graph()
       .setNode("a", { rank: 0 })
       .setNode("b", { rank: 1 })
       .setNode("c", { rank: 2 })
@@ -23,7 +23,7 @@ describe("feasibleTree", () => {
       .setPath(["a", "b", "c"], { minlen: 1 })
       .setEdge("a", "d", { minlen: 1 });
 
-    var tree = feasibleTree(g);
+    let tree = feasibleTree(g);
     expect(g.node("b").rank).to.eql(g.node("a").rank + 1);
     expect(g.node("c").rank).to.eql(g.node("b").rank + 1);
     expect(g.node("d").rank).to.eql(g.node("a").rank + 1);
@@ -34,7 +34,7 @@ describe("feasibleTree", () => {
   });
 
   it("correctly shortens slack by pulling a node down", () => {
-    var g = new Graph()
+    let g = new Graph()
       .setNode("a", { rank: 2 })
       .setNode("b", { rank: 0 })
       .setNode("c", { rank: 2 })