jest expect an error code example

Example 1: jest expect error to be thrown

test("Test description", () => {
  const t = () => {
    throw new TypeError();
  };
  expect(t).toThrow(TypeError);
});

Example 2: expect any function jest

expect(something).toEqual(expect.any(Function))

Example 3: Jest toContain

# 1. Use '.toContain' when you want to check that an item is in an array.
# 2 '.toContain' can also check whether a string is a substring of another string.
test('the flavor list contains lime', () => {
  expect(['lime', 'mangle']).toContain('lime');
});

test('the flavor list contains lime', () => {
  expect("lime juice").toContain('lime');
});