index.test.js

const sut = require(".");

describe("Redirect", () => {
  test("When not given res, should throw error", () => {
    // Arrange
    // Act
    expect(() => sut())
      // Assert
      .toThrowError("Response object required");
  });

  test("When not given status code, should throw error", () => {
    // Arrange
    // Act
    expect(() => sut({}))
      // Assert
      .toThrowError("Status code required");
  });

  test("When not given location, should throw error", () => {
    // Arrange
    // Act
    expect(() => sut({}, 300))
      // Assert
      .toThrowError("Location required");
  });

  test("When given all args, should set statusCode and location", () => {
    // Arrange
    const statusCode = 302;
    const location = "http://google.com";
    const res = {
      setHeader: jest.fn(),
      end: jest.fn()
    };

    // Act
    sut(res, statusCode, location);

    // Assert
    expect(res.statusCode).toBe(statusCode);
    expect(res.setHeader).toHaveBeenCalledWith("Location", location);
    expect(res.end).toHaveBeenCalled();
  });
});