Add include_hidden option to check box collection

This option defaults to true and allows developers to control whether or
not a hidden field is injected into their collection of check boxes.

Refs #238

lib/govuk_design_system_formbuilder/builder.rb

@@ -646,6 +646,7 @@ def govuk_radio_divider(text = config.default_radio_divider_text)
     # @param form_group [Hash] configures the form group
     # @option form_group classes [Array,String] sets the form group's classes
     # @option form_group kwargs [Hash] additional attributes added to the form group
+    # @param include_hidden [Boolean] controls whether a hidden field is inserted to allow for empty submissions
     # @param block [Block] any HTML passed in will be injected into the fieldset, after the hint and before the checkboxes
     # @return [ActiveSupport::SafeBuffer] HTML output
     #
@@ -682,7 +683,7 @@ def govuk_radio_divider(text = config.default_radio_divider_text)
     #    :name,
     #    legend: -> { tag.h3('What kind of sandwich do you want?') }
     #
-    def govuk_collection_check_boxes(attribute_name, collection, value_method, text_method, hint_method = nil, hint: {}, legend: {}, caption: {}, small: false, classes: nil, form_group: {}, &block)
+    def govuk_collection_check_boxes(attribute_name, collection, value_method, text_method, hint_method = nil, hint: {}, legend: {}, caption: {}, small: false, classes: nil, form_group: {}, include_hidden: true, &block)
       Elements::CheckBoxes::Collection.new(
         self,
         object_name,
@@ -697,6 +698,7 @@ def govuk_collection_check_boxes(attribute_name, collection, value_method, text_
         small: small,
         classes: classes,
         form_group: form_group,
+        include_hidden: include_hidden,
         &block
       ).html
     end

lib/govuk_design_system_formbuilder/elements/check_boxes/collection.rb

@@ -6,19 +6,20 @@ class Collection < Base
         include Traits::Hint
         include Traits::Supplemental
 
-        def initialize(builder, object_name, attribute_name, collection, value_method:, text_method:, hint:, legend:, caption:, small:, classes:, form_group:, hint_method: nil, &block)
+        def initialize(builder, object_name, attribute_name, collection, value_method:, text_method:, hint:, legend:, caption:, small:, classes:, form_group:, include_hidden:, hint_method: nil, &block)
           super(builder, object_name, attribute_name, &block)
 
-          @collection   = collection
-          @value_method = value_method
-          @text_method  = text_method
-          @hint_method  = hint_method
-          @small        = small
-          @legend       = legend
-          @caption      = caption
-          @hint         = hint
-          @classes      = classes
-          @form_group   = form_group
+          @collection     = collection
+          @value_method   = value_method
+          @text_method    = text_method
+          @hint_method    = hint_method
+          @small          = small
+          @legend         = legend
+          @caption        = caption
+          @hint           = hint
+          @classes        = classes
+          @form_group     = form_group
+          @include_hidden = include_hidden
         end
 
         def html
@@ -56,7 +57,7 @@ def check_boxes
         def collection
           link_errors = has_errors?
 
-          @builder.collection_check_boxes(@attribute_name, @collection, @value_method, @text_method) do |check_box|
+          @builder.collection_check_boxes(@attribute_name, @collection, @value_method, @text_method, include_hidden: @include_hidden) do |check_box|
             Elements::CheckBoxes::CollectionCheckBox.new(
               @builder,
               @object_name,

spec/govuk_design_system_formbuilder/builder/check_boxes/collection_spec.rb

@@ -66,6 +66,10 @@
         end
       end
 
+      specify 'a hidden field is present by default' do
+        expect(subject).to have_tag('input', with: { type: 'hidden', name: "#{object_name}[#{attribute}][]" })
+      end
+
       context 'check box size' do
         context 'when small is specified in the options' do
           subject { builder.send(*args, small: true) }
@@ -156,6 +160,14 @@
       it_behaves_like 'a collection field that supports setting the value via a proc' do
         let(:attribute) { :favourite_colour }
       end
+
+      context 'suppressing the hidden field' do
+        subject { builder.send(*args, include_hidden: false) }
+
+        specify "the hidden field should be present within the fieldset" do
+          expect(subject).not_to have_tag('input', with: { type: 'hidden' })
+        end
+      end
     end
   end
 end