erb_template.rb

#!/usr/bin/env ruby

require 'minitest/autorun'

require 'erb'

class ErbTemplate
  def initialize(hash)
    hash.each do |k, v|
      instance_var = "@#{k}"
      instance_variable_set(instance_var, v)
      define_singleton_method(k) { instance_variable_get(instance_var) }
    end
  end

  def render(template)
    ERB.new(template).result(binding)
  end

  def self.render(template, hash)
    new(hash).render(template)
  end
end

describe ErbTemplate do
  it 'should render ERB' do
    expected = 'foo bar'
    actual = ErbTemplate.render('<%= foo %> <%= bar %>', foo: :foo, bar: :bar)
    actual.must_equal expected
  end

  it 'should throw exceptions for undefined variables' do
    -> { ErbTemplate.render('<%= foo %>', bar: :bar) }.must_raise NameError
  end
end

erb_template_fail.rb

#!/usr/bin/env ruby

require 'minitest/autorun'

require 'erb'
require 'ostruct'

class ErbTemplateFail < OpenStruct
  def render(template)
    ERB.new(template).result(binding)
  end

  def self.render(template, hash)
    new(hash).render(template)
  end
end

describe ErbTemplateFail do
  it 'should render ERB' do
    expected = 'foo bar'
    actual = ErbTemplateFail.render('<%= foo %> <%= bar %>', foo: :foo, bar: :bar)
    actual.must_equal expected
  end

  it 'should throw exceptions for undefined variables' do
    -> { ErbTemplateFail.render('<%= foo %>', bar: :bar) }.must_raise NameError
  end
end