How would one test a custom Padrino FormBuilder?

Question

Suppose we have a custom FormBuilder in Padrino, like the following:

class CustomFormBuilder < Padrino::Helpers::FormBuilder::AbstractFormBuilder
  def foo(arg1, arg2, ...)
    # do something with #template
  end
end

What's the right way to test this?

It seems like the correct thing to do would be something like:

describe CustomFormBuilder do
  it "renders the right output"
    # ...
    result = CustomFormBuilder.new(...).template.render

    expect(result).to include 'expected-content'
  end
end

It's not clear to me how to pull that off:

• Usually the framework instantiates the FormBuilders, so it feels wrong that I'm doing it here. Is there a better approach?
• I don't know how to pass an object that the FormBuilder will accept as a template.
• I don't know how to get the result of rendering the template.

What's the right way to test this?

Answer 1

I figured this out after some effort. The idea is to make an object which represents the template, pass that to the FormBuilder, make another object for the model, and then see if the builder generates the correct HTML.

describe CustomFormBuilder do
  let(:template) do
    Class.new do
      include Padrino::Helpers::OutputHelpers
      include Padrino::Helpers::FormHelpers
      include Padrino::Helpers::TagHelpers
    end.new
  end

  it "makes a class" do
    model    = Class.new { include ActiveModel::Model }.new
    builder  = described_class.new template, model

    expect(builder.helper_method :foo).to include 'class="expected-class"'

    # or, if you're using rspec-html-matchers or something similar...
    expect(builder.helper_method :foo).to \
      have_tag('div', :with => { :class => 'bar' })
  end
end