def strip_invisible_chars
    Util::Strings.strip_control_chars(params)
  end

describe '#strip_invisible_chars' do
    let(:some) { {two: "three"} }

    subject { controller.send :strip_invisible_chars }

    before { allow(Util::Strings).to receive(:strip_control_chars).with(:params).and_return(:some) }

    context 'yes' do
      let(:params) { {one: "two"} }

      it 'returns result' do
        byebug
        expect(response.status).to eq 200
      end
    end

    context 'no' do
      let(:params) {}

      it 'returns result' do
        expect(response.status).to eq 400
      end
    end
  end