Fixed bug in FACT function. Issue: #2238 (#2242)

Author: karlkallman

src/EPPlus/FormulaParsing/Excel/Functions/MathFunctions/Fact.cs

@@ -32,7 +32,7 @@ public override CompileResult Execute(IList<FunctionArgument> arguments, Parsing
             if (e1 != null) return CompileResult.GetErrorResult(e1.Type);
             if (number < 0) return CompileResult.GetErrorResult(eErrorType.NA);
             var result = 1d;
-            for (var x = 1; x < number; x++)
+            for (var x = 1; x <= number; x++)
             {
                 result *= x;
             }

src/EPPlusTest/FormulaParsing/IntegrationTests/BuiltInFunctions/MathFunctionsTests.cs

@@ -34,6 +34,7 @@ Date               Author                       Change
 using OfficeOpenXml.FormulaParsing;
 using OfficeOpenXml;
 using FakeItEasy;
+using FakeItEasy.Configuration;
 
 namespace EPPlusTest.FormulaParsing.IntegrationTests.BuiltInFunctions
 {
@@ -561,6 +562,13 @@ public void FactShouldReturnAResult()
             Assert.AreEqual(1d, result);
         }
 
+        [TestMethod]
+        public void FactShouldReturnCorrectResult()
+        {
+            var result = _parser.Parse("Fact(5)");
+            Assert.AreEqual(120d, result);
+        }
+
         [TestMethod]
         public void FactDoubleShouldReturnAResult()
         {