Add testcase - traverse - edge cases like rendering divs directly as root

test/traverse-edge.spec.tsx

@@ -0,0 +1,32 @@
+// import * as React from "react";
+
+// Import stuff from src
+import { traverse } from "../src";
+
+// Import test helpers and sample components
+import { mountAndGetRootNode } from "./utils/mount-in-enzyme";
+
+describe("traverse", () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.body.appendChild(document.createElement("div"));
+  });
+
+  afterEach(() => {
+    document.body.removeChild(container);
+  });
+
+  describe("edge cases", () => {
+    it("should work for string nodes", () => {
+      const rootNode = mountAndGetRootNode('div', container);
+      const mockCallback = jest.fn();
+
+      traverse(rootNode, mockCallback);
+
+      // Can't be zero, in any case
+      expect(mockCallback.mock.calls.length).not.toBe(0);
+      expect(mockCallback.mock.calls.length).toBe(1);
+    });
+  });
+});