old_contents: import Kasen from "../src/kasen";
  import KasenArray from "../src/collection/array";
  import KasenObject from "../src/collection/object";
  
  describe("Kasen", () => {
    test("ok", () => {
      expect(Kasen([])).toBeInstanceOf(KasenArray);
      expect(Kasen({})).toBeInstanceOf(KasenObject);
    });
  
    test("error", () => {
      expect(() => Kasen()).toThrow(TypeError);
      expect(() => Kasen(null)).toThrow(TypeError);
    });
  
    describe("copy()", () => {
      test("error", () => {
        expect(() => Kasen.copy()).toThrow(TypeError);
        expect(() => Kasen.copy(null)).toThrow(TypeError);
      });
    });
  });
  
new_contents: import Kasen from "../src/kasen";
  import KasenArray from "../src/collection/array";
  import KasenObject from "../src/collection/object";
  
  describe("Kasen", () => {
    test("ok", () => {
      expect(Kasen([])).toBeInstanceOf(KasenArray);
      expect(Kasen({})).toBeInstanceOf(KasenObject);
    });
  
    test("error", () => {
      expect(() => Kasen()).toThrow(TypeError);
      expect(() => Kasen(null)).toThrow(TypeError);
    });
  
    describe("copy()", () => {
      test("error", () => {
        expect(() => Kasen.copy()).toThrow(TypeError);
        expect(() => Kasen.copy(null)).toThrow(TypeError);
      });
    });
  
    describe("isEmpty()", () => {
      test("error", () => {
        expect(() => Kasen.isEmpty()).toThrow(TypeError);
        expect(() => Kasen.isEmpty(null)).toThrow(TypeError);
      });
    });
  
    describe("toArray()", () => {
      test("error", () => {
        expect(() => Kasen.toArray()).toThrow(TypeError);
        expect(() => Kasen.toArray(null)).toThrow(TypeError);
      });
    });
  
    describe("toObject()", () => {
      test("error", () => {
        expect(() => Kasen.toObject()).toThrow(TypeError);
        expect(() => Kasen.toObject(null)).toThrow(TypeError);
      });
    });
  
    describe("keys()", () => {
      test("error", () => {
        expect(() => Kasen.keys()).toThrow(TypeError);
        expect(() => Kasen.keys(null)).toThrow(TypeError);
      });
    });
  
    describe("values()", () => {
      test("error", () => {
        expect(() => Kasen.values()).toThrow(TypeError);
        expect(() => Kasen.values(null)).toThrow(TypeError);
      });
    });
  
    describe("entries()", () => {
      test("error", () => {
        expect(() => Kasen.entries()).toThrow(TypeError);
        expect(() => Kasen.entries(null)).toThrow(TypeError);
      });
    });
  });
  
subject: Add tests for validation of collection