Add Person validation

app/models/person.rb

@@ -1,2 +1,20 @@
 class Person < ApplicationRecord
+  validates :email, presence: true, uniqueness: true
+  validates :first_name, presence: true
+  validates :last_name, presence: true
+  validates :is_admin, presence: true
+
+  validate :birth_date_cannot_be_in_future
+
+  before_validation :not_admin_if_nil
+
+  def birth_date_cannot_be_in_future
+    if self.birth_date > Date.today
+      errors.add(:birth_date, "can't be in the future.")
+    end
+  end
+
+  def not_admin_if_nil
+    self.is_admin ||= false
+  end
 end