getUserName.spec.ts

function getUserName(user: { name?: string; fullName: string }) {
  return user.name || user.fullName.split(' ')[0];
}

describe('getUserName', () => {
  it('should return name if it exists', () => {
    const name = 'name';
    const result = getUserName({ name } as any);
    // TypeScript would error  ^^^^^^^^
    // if we didn't cast it
    expect(result).toBe(name);
  });
});