t.js

describe("The RPN expression evaluator", () => {
  it("should return null when the expression is an empty string", () => {
    const result = RPN("");
    expect(result).toBeNull();
  });
  it("should return the same value when the expression holds a single value", () => {
    const result = RPN("42");
    expect(result).toBe(42);
  });
  it("should properly calculate an expression", () => {
    const result = RPN("5 1 2 + 4 * - 10 /");
    expect(result).toBe(-0.7);
  });
  it("should throw an error whenever an invalid expression is passed", () => {
    const compute = () => RPN("1 + - 1");
    expect(compute).toThrow();
  });
});