custom_assert_01.ex

test "age is required" do
  # Create changeset
  params = %{"name" => "tyler"}
  changset = Person.changeset(%Person{}, params)
  
  # Changeset should be invalid
  assert changeset.valid? == false

  # Find the error message for the invalid field
  error_message = Keyword.get(changeset.errors, :age)

  # Make sure that the error message is useful and polite
  assert error_message =~ "blank"
  assert error_message =~ "please"
end