diff --git a/Flow.Launcher.Test/Flow.Launcher.Test.csproj b/Flow.Launcher.Test/Flow.Launcher.Test.csproj
index 1164e5ebe..11ccff05b 100644
--- a/Flow.Launcher.Test/Flow.Launcher.Test.csproj
+++ b/Flow.Launcher.Test/Flow.Launcher.Test.csproj
@@ -39,6 +39,7 @@
   </ItemGroup>
   
   <ItemGroup>
+    <ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Calculator\Flow.Launcher.Plugin.Calculator.csproj" />
     <ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Explorer\Flow.Launcher.Plugin.Explorer.csproj" />
     <ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Program\Flow.Launcher.Plugin.Program.csproj" />
     <ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Url\Flow.Launcher.Plugin.Url.csproj" />
diff --git a/Flow.Launcher.Test/Plugins/CalculatorTest.cs b/Flow.Launcher.Test/Plugins/CalculatorTest.cs
new file mode 100644
index 000000000..3f403b24e
--- /dev/null
+++ b/Flow.Launcher.Test/Plugins/CalculatorTest.cs
@@ -0,0 +1,86 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using Flow.Launcher.Plugin.Calculator;
+using Mages.Core;
+using NUnit.Framework;
+using NUnit.Framework.Legacy;
+
+namespace Flow.Launcher.Test.Plugins
+{
+    [TestFixture]
+    public class CalculatorPluginTest
+    {
+        private readonly Main _plugin;
+
+        public CalculatorPluginTest()
+        {
+            _plugin = new Main();
+            
+            var settingField = typeof(Main).GetField("_settings", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (settingField == null)
+                Assert.Fail("Could not find field '_settings' on Flow.Launcher.Plugin.Calculator.Main");
+            settingField.SetValue(_plugin, new Settings
+            {
+                ShowErrorMessage = false // Make sure we return the empty results when error occurs
+            });
+
+            var engineField = typeof(Main).GetField("MagesEngine", BindingFlags.NonPublic | BindingFlags.Static);
+            if (engineField == null)
+                Assert.Fail("Could not find static field 'MagesEngine' on Flow.Launcher.Plugin.Calculator.Main");
+            engineField.SetValue(null, new Engine(new Configuration
+            {
+                Scope = new Dictionary<string, object>
+                {
+                    { "e", Math.E }, // e is not contained in the default mages engine
+                }
+            }));
+        }
+
+        // Basic operations
+        [TestCase(@"1+1", "2")]
+        [TestCase(@"2-1", "1")]
+        [TestCase(@"2*2", "4")]
+        [TestCase(@"4/2", "2")]
+        [TestCase(@"2^3", "8")]
+        // Decimal places
+        [TestCase(@"10/3", "3.3333333333")]
+        // Parentheses
+        [TestCase(@"(1+2)*3", "9")]
+        [TestCase(@"2^(1+2)", "8")]
+        // Functions
+        [TestCase(@"pow(2,3)", "8")]
+        [TestCase(@"min(1,-1,-2)", "-2")]
+        [TestCase(@"max(1,-1,-2)", "1")]
+        [TestCase(@"sqrt(16)", "4")]
+        [TestCase(@"sin(pi)", "0")]
+        [TestCase(@"cos(0)", "1")]
+        [TestCase(@"tan(0)", "0")]
+        [TestCase(@"log(100)", "2")]
+        [TestCase(@"ln(e)", "1")]
+        [TestCase(@"abs(-5)", "5")]
+        // Constants
+        [TestCase(@"pi", "3.1415926536")]
+        // Complex expressions
+        [TestCase(@"(2+3)*sqrt(16)-log(100)/ln(e)", "19")]
+        [TestCase(@"sin(pi/2)+cos(0)+tan(0)", "2")]
+        // Error handling (should return empty result)
+        [TestCase(@"10/0", "")]
+        [TestCase(@"sqrt(-1)", "")]
+        [TestCase(@"log(0)", "")]
+        [TestCase(@"invalid_expression", "")]
+        public void CalculatorTest(string expression, string result)
+        {
+            ClassicAssert.AreEqual(GetCalculationResult(expression), result);
+        }
+
+        private string GetCalculationResult(string expression)
+        {
+            var results = _plugin.Query(new Plugin.Query()
+            {
+                Search = expression
+            });
+            return results.Count > 0 ? results[0].Title : string.Empty;
+        }
+    }
+}
diff --git a/Plugins/Flow.Launcher.Plugin.Calculator/Main.cs b/Plugins/Flow.Launcher.Plugin.Calculator/Main.cs
index 17b4a85a4..42cbafb43 100644
--- a/Plugins/Flow.Launcher.Plugin.Calculator/Main.cs
+++ b/Plugins/Flow.Launcher.Plugin.Calculator/Main.cs
@@ -112,7 +112,8 @@ namespace Flow.Launcher.Plugin.Calculator
                             Title = newResult,
                             IcoPath = IcoPath,
                             Score = 300,
-                            SubTitle = Localize.flowlauncher_plugin_calculator_copy_number_to_clipboard(),
+                            // Check context nullability for unit testing
+                            SubTitle = Context == null ? string.Empty : Localize.flowlauncher_plugin_calculator_copy_number_to_clipboard(),
                             CopyText = newResult,
                             Action = c =>
                             {