Example specs for JSON Patch implementation in Rails model

json_patch_spec.rb

# See: https://formapi.io/blog/posts/json-patch-with-rails-5-and-react/

require 'spec_helper'

describe Template do
  describe 'applying JSON patches' do
    let(:template) {
      FactoryGirl.create(:template,
        template_type: 'pdf',
        fields: {
          1 => {
            x: 100,
          },
          2 => {
            x: 100,
          }
        }
      )
    }

    context "fields" do
      it 'should apply a patch during update_attributes' do
        template.update_attributes(
          fields_patch: [{"op"=>"replace", "path"=>"/1/x", "value"=>150}]
        )
        expect(template.valid?).to eq true
        expect(template.errors).to be_blank
        expect(template.fields['1']['x']).to eq 150
      end

      it 'should add a validation error if the patch was not an array' do
        template.update_attributes(
          fields_patch: "/1/x"
        )
        expect(template.valid?).to eq false
        expect(template.errors).to be_present
        expect(template.errors[:fields].first).to include 'was not an array'
        expect(template.fields['1']['x']).to eq 100
      end

      it 'should add a validation error if the patch cannot be applied' do
        template.update_attributes(
          fields_patch: [{"op"=>"replace", "path"=>"/missing/x", "value"=>150}]
        )
        expect(template.valid?).to eq false
        expect(template.errors).to be_present
        expect(template.errors[:fields].first).to include 'Could not apply JSON patch'
      end

      it 'should apply a patch manually' do
        template.fields_patch = [{"op"=>"replace", "path"=>"/1/x", "value"=>false}]
        expect(template.changed?).to eq true
        expect(template.valid?).to eq true
        expect(template.errors).to be_blank
        expect(template.fields['1']['x']).to eq false
      end

      it 'should clear errors on reload' do
        template.fields_patch = [{"op"=>"replace", "path"=>"/missing/x", "value"=>false}]
        expect(template.valid?).to eq false
        expect(template.errors[:fields]).to be_present
        template.reload
        expect(template.valid?).to eq true
        expect(template.errors).to_not be_present
      end
    end
  end
end