ActiveModel Validation With Whitespace

validation.rb

#!/usr/bin/env ruby

require 'active_model'
require 'minitest/autorun'

class Simple
  include ActiveModel::Model
  validates :name, allow_blank: true, allow_nil: true, length: { is: 2 }
  attr_accessor :name

  # This approach could be fixed by using a `before_validation` method to strip
  # whitespace if it's desired to allow the user to accidentally add extraneous
  # whitespace.
end

class Precise
  include ActiveModel::Model
  validates :name, allow_nil: true, format: { with: /\A(\w{2})?\z/ }
  attr_accessor :name
end

class TestExample < Minitest::Test
  def test_simple
    assert_predicate Simple.new(name: nil), :valid?
    assert_predicate Simple.new(name: ''), :valid?
    assert_predicate Simple.new(name: 'AB'), :valid?
    assert_predicate Simple.new(name: 'AB'), :valid?

    # The following two cases fall under the `allow_blank` case.
    # When the model is backed by ActiveRecord, the whitespace will be saved
    # to the database.
    assert_predicate Simple.new(name: ' '), :valid?
    assert_predicate Simple.new(name: '  '), :valid?

    # These are all ones we expect to fail
    refute_predicate Simple.new(name: 'A'), :valid?
    refute_predicate Simple.new(name: 'ABC'), :valid?
    refute_predicate Simple.new(name: 'AB '), :valid?
    refute_predicate Simple.new(name: ' AB'), :valid?

    # These are unexpected valid cases
    assert_predicate Simple.new(name: 'A '), :valid?
    assert_predicate Simple.new(name: ' B'), :valid?
  end

  def test_precise
    # These validations are the same as before
    assert_predicate Precise.new(name: nil), :valid?
    assert_predicate Precise.new(name: ''), :valid?
    assert_predicate Precise.new(name: 'AB'), :valid?
    assert_predicate Precise.new(name: 'AB'), :valid?

    refute_predicate Simple.new(name: 'A'), :valid?
    refute_predicate Simple.new(name: 'ABC'), :valid?
    refute_predicate Simple.new(name: 'AB '), :valid?
    refute_predicate Simple.new(name: ' AB'), :valid?

    # These validations differ from before, and are what is expected
    refute_predicate Precise.new(name: ' '), :valid?
    refute_predicate Precise.new(name: '  '), :valid?
    refute_predicate Precise.new(name: 'A '), :valid?
    refute_predicate Precise.new(name: ' B'), :valid?
  end
end