Migrate .NET Project to F#

FSharp/Calculator/Calc.fs

@@ -0,0 +1,9 @@
+module Calculator
+
+let sum a b = a + b
+
+let subtract a b = a - b
+
+let multiply a b = a * b
+
+let divide a b = a / b

FSharp/CalculatorTest/TestCalculator.fs

@@ -0,0 +1,28 @@
+module TestCalculator
+
+open NUnit.Framework
+open FsUnit
+open Calculator
+
+[<TestFixture>]
+type TestCalculator() =
+
+    [<OneTimeSetUp>]
+    member this.Setup() = printfn "Starting Calculator tests"
+
+    [<OneTimeTearDown>]
+    member this.TearDown() = printfn "Calculator tests are finished"
+
+    [<Test>]
+    [<Category("SumTests")>]
+    member this.OneCanSumPositiveIntegers() = Calc.sum 5 5 |> should equal 10
+
+    [<Test>]
+    [<Category("SumTests")>]
+    member this.OneCanSumNegativeIntegers() = Calc.sum -5 -5 |> should equal -10
+
+    [<Test>]
+    [<Category("SubtractTests")>]
+    member this.OneCanSubtractPositiveIntegers() = Calc.subtract 5 5 |> should equal 0
+
+    // Remaining test cases translated similarly