Refactor test mounting logic to separate file

test/utils/mount-in-enzyme.tsx

@@ -0,0 +1,33 @@
+import * as React from "react";
+import { mount } from "enzyme";
+import { FiberNode } from '../../src/mocked-types';
+
+export class RootNodeNotFoundError extends Error {
+  static message = `Couldn't find root node. This might occur if render has become async`
+  constructor() {
+    super(RootNodeNotFoundError.message);
+    this.name = "RootNodeNotFoundError";
+  }
+}
+
+export function mountAndGetRootNode(
+  SomeComponentClass: typeof React.Component,
+  container: HTMLElement
+) {
+  const rootRef = React.createRef<React.Component>();
+
+  // TODO: later make this async as mount might be async and hence next steps will fail
+  mount(<SomeComponentClass ref={rootRef} />, { attachTo: container });
+
+  if (rootRef.current === null) {
+    throw new RootNodeNotFoundError();
+  }
+
+  const rootNode = ((rootRef.current as any)._reactInternalFiber as FiberNode).child;
+
+  if (rootNode === null) {
+    throw new RootNodeNotFoundError();
+  }
+
+  return rootNode;
+}