Selector Example with Currying and Selector Unit Tests

counterWithSelector.tsx

import React from "react";
import { useSelector } from "react-redux";
import {selectCountFormatted} from './selectors'

export const Counter = () => {
  const countFormattedAsDollars = useSelector(selectCountFormatted('$'));
  
...

selectors.spec.ts

describe("counter selectors", () => {
  const state: RootState = {
    counter: {
      value: 3,
      status: "idle",
    },
  };

  it("should format count in dollars", () => {
    const actual = selectCountFormatted("$")(state);
    expect(actual).toEqual("$3");
  });

  it("should format count as a percentage", () => {
    const actual = selectCountFormatted("%")(state);
    expect(actual).toEqual("3%");
  });

  it("should select multiple items from state", () => {
    const actual = selectCountAndStatus(state);
    expect(actual).toEqual("The current count is 3 and the status is idle");
  });
});