Added calculation service helper test

spec/helpers/calculators/calculation_service_helper_spec.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Calculators::CalculationService, type: :helper do
+    let(:calculator) { instance_double("Calculator", formulas: formulas) }
+    let(:formulas) do
+      [
+        instance_double("Formula", expression: "x + y", en_label: "Addition", en_unit: "units", uk_label: "Додавання", uk_unit: "одиниці"),
+        instance_double("Formula", expression: "x * y", en_label: "Multiplication", en_unit: "units", uk_label: "Множення", uk_unit: "одиниці")
+      ]
+    end
+    let(:inputs) { ActionController::Parameters.new({ x: 5, y: 3 }) }
+
+    before do
+      allow_any_instance_of(ApplicationHelper).to receive(:current_locale?).with(:en).and_return(locale_en)
+    end
+
+    describe "#perform" do
+      subject { described_class.new(calculator, inputs).perform }
+
+      context "when locale is English" do
+        let(:locale_en) { true }
+
+        it "returns results with English labels and units" do
+          expect(subject).to eq([
+            { label: "Addition", result: 8, en_unit: "units" },
+            { label: "Multiplication", result: 15, en_unit: "units" }
+          ])
+        end
+      end
+
+      context "when locale is Ukrainian" do
+        let(:locale_en) { false }
+
+        it "returns results with Ukrainian labels and units" do
+          expect(subject).to eq([
+            { label: "Додавання", result: 8, en_unit: "одиниці" },
+            { label: "Множення", result: 15, en_unit: "одиниці" }
+          ])
+        end
+      end
+    end
+  end
+