Add testcase - findNodeByComponentRef-negative

Check cases where ref is not found in fiber tree

test/findNodeByComponentRef-negative.spec.tsx

@@ -0,0 +1,95 @@
+import * as React from "react";
+
+// Import stuff from src
+import { findNodeByComponentRef } from "../src";
+import { mountAndGetRootNode } from "./utils/mountInEnzyme";
+import getWrappedComponent from "./utils/getWrappedComponent";
+
+class RandomClass extends React.Component {
+  render() {
+    return <div></div>;
+  }
+}
+
+// Import test helpers and sample components
+
+describe("findNodeByComponentRef", () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.body.appendChild(document.createElement("div"));
+  });
+
+  afterEach(() => {
+    document.body.removeChild(container);
+  });
+
+  describe("negative", () => {
+    it("should not work for 2nd-level class", () => {
+      const C2Ref = React.createRef<C2>();
+
+      class C1 extends React.Component {
+        render() {
+          return <C2 ref={C2Ref} />;
+        }
+      }
+      class C2 extends React.Component {
+        render() {
+          return <div>C2 here</div>;
+        }
+      }
+      const WrappedC = getWrappedComponent(C1);
+      const rootNode = mountAndGetRootNode(WrappedC, container);
+
+      if (C2Ref.current === null) {
+        throw new Error("Ref is not yet set");
+      }
+
+      const foundSame = findNodeByComponentRef(rootNode, new C2({}));
+      const foundDiff = findNodeByComponentRef(rootNode, new RandomClass({}));
+
+      expect(foundSame).toBeFalsy();
+      expect(foundSame).toBe(null);
+      expect(foundDiff).toBeFalsy();
+      expect(foundDiff).toBe(null);
+    });
+
+    it("should work for 5th-level class", () => {
+      const C2Ref = React.createRef<C2>();
+
+      class C1 extends React.Component {
+        render() {
+          return (
+            <div>
+              <div>
+                <span></span>
+                <C2 ref={C2Ref}></C2>
+              </div>
+            </div>
+          );
+        }
+      }
+
+      class C2 extends React.Component {
+        render() {
+          return <a href="google.com">Fn2 here</a>;
+        }
+      }
+
+      const WrappedC = getWrappedComponent(C1);
+      const rootNode = mountAndGetRootNode(WrappedC, container);
+
+      if (C2Ref.current === null) {
+        throw new Error("Ref is not yet set");
+      }
+
+      const foundSame = findNodeByComponentRef(rootNode, new C2({}));
+      const foundDiff = findNodeByComponentRef(rootNode, new RandomClass({}));
+
+      expect(foundSame).toBeFalsy();
+      expect(foundSame).toBe(null);
+      expect(foundDiff).toBeFalsy();
+      expect(foundDiff).toBe(null);
+    });
+  });
+});