describe("filter", () => {
  const array = ["nakanishi", "john", "jimmy"];

  it("all true", () => {
    const res = array.filter(person => {
      return true;
    });
    expect(res).toEqual(["nakanishi", "john", "jimmy"]);
  });

  it("all false", () => {
    const res = array.filter(person => {
      return false;
    });
    expect(res).toEqual([]);
  });

  it("naknishi", () => {
    const res = array.filter(person => {
      return person === "nakanishi";
    });
    expect(res).toEqual(["nakanishi"]);
  });

  it("length", () => {
    const res = array.filter(person => {
      return person.length > 4;
    });
    expect(res).toEqual(["nakanishi", "jimmy"]);
  });
});