#user.rb
class User < ApplicationRecord
  validates_presence_of [:first_name, :last_name, :email, :password]
end

# bad
# user_spec.rb
describe "#full_name" do
  it "Concantenate firstname and last name" do
    user = User.new(
      first_name: "Burhanudin",
      last_name: "Hakim",
      email: "burhanudin@me.com",
      password: "password"
    )

    expect(user.full_name).to eq("Burhanudin Hakim")
  end
end

# good

# spec/factories.rb
FactoryBot.define do
  factory :user do
    first_name { "Burhanudin" }
    last_name { "Hakim" }
    email { "burhanudin@me.com" }
    password { "secret" }
end

#user_spec.rb
describe "#full_name" do
  it "Concantenate firstname and last name" do
    user = build(:user, first_name: "Burhanudin", last_name: "Hakim")

    expect(user.full_name).to eq("Burhanudin Hakim")
  end
end