Create unit tests for Calculator plugin (#6356)

* Refactored logic and made it unit testable

* Changes after code review

* Added to build steps, and modified bracket to new class with unittest. Validates complexer cases now.

Co-authored-by: p-storm <paul.de.man@gmail.com>

src/modules/launcher/Plugins/Microsoft.Plugin.Calculator/CalculateEngine.cs

@@ -0,0 +1,68 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Globalization;
+using Mages.Core;
+
+namespace Microsoft.Plugin.Calculator
+{
+    public class CalculateEngine
+    {
+        private readonly Engine _magesEngine = new Engine();
+        public const int RoundingDigits = 10;
+
+        public CalculateResult Interpret(string input)
+        {
+            return Interpret(input, CultureInfo.CurrentCulture);
+        }
+
+        public CalculateResult Interpret(string input, CultureInfo cultureInfo)
+        {
+            if (!CalculateHelper.InputValid(input))
+            {
+                return default;
+            }
+
+            var result = _magesEngine.Interpret(input);
+
+            // This could happen for some incorrect queries, like pi(2)
+            if (result == null)
+            {
+                return default;
+            }
+
+            result = TransformResult(result);
+
+            if (string.IsNullOrEmpty(result?.ToString()))
+            {
+                return default;
+            }
+
+            var decimalResult = Convert.ToDecimal(result, cultureInfo);
+            var roundedResult = Math.Round(decimalResult, RoundingDigits, MidpointRounding.AwayFromZero);
+
+            return new CalculateResult()
+            {
+                Result = decimalResult,
+                RoundedResult = roundedResult,
+            };
+        }
+
+        private static object TransformResult(object result)
+        {
+            if (result.ToString() == "NaN")
+            {
+                return Properties.Resources.wox_plugin_calculator_not_a_number;
+            }
+
+            if (result is Function)
+            {
+                return Properties.Resources.wox_plugin_calculator_expression_not_complete;
+            }
+
+            return result;
+        }
+    }
+}