contains.test.js

const contains = require("./contains.js");

/*
Implement a function called contains that checks an object contains a
particular property

E.g. contains({a: 1, b: 2}, 'a') // returns true
as the object contains a key of 'a'

E.g. contains({a: 1, b: 2}, 'c') // returns false
as the object doesn't contains a key of 'c'
*/

// Acceptance criteria:

// Given a contains function
// When passed an object and a property name
// Then it should return true if the object contains the property, false otherwise
test("returns true if the object contains the property, false otherwise", () => {
  const obj = { a: 1, b: 2 };

  expect(contains(obj, "a")).toBe(true);   // existing property
  expect(contains(obj, "b")).toBe(true);   // existing property
  expect(contains(obj, "c")).toBe(false);  // non‑existent property
});



// Given an empty object
// When passed to contains
// Then it should return false
test("contains on empty object returns false", () => {
    expect(contains({}, "a")).toBe(false);
  });


// Given an object with properties
// When passed to contains with an existing property name
// Then it should return true
test("contains on object with existing property returns true", () => {
    expect(contains({a: 1, b: 2}, "a")).toBe(true);
  });
// Given an object with properties
// When passed to contains with a non-existent property name
// Then it should return false
test("contains on object with non-existent property returns false", () => {
    expect(contains({a: 1, b: 2}, "c")).toBe(false);
  });

// Given invalid parameters like an array
// When passed to contains
// Then it should return false or throw an error

  test("contains on invalid parameters returns false", () => {
  // We use an index that EXISTS in the array (0)
  // If the function returns false, we know it's because it rejected the ARRAY type
  expect(contains(["test"], 0)).toBe(false);
  expect(contains(null, "a")).toBe(false);
});