Added F# starter solution based on .NET Core

fsharp-core/GildedRose.ApprovalTests/Tests.fs

@@ -0,0 +1,19 @@
+module GildedRose.ApprovalTests
+
+open System
+open Xunit
+open System.Text
+open System.IO
+
+[<Fact>]
+let ``Thirty day report is correct`` () =
+    let expected = File.ReadAllText "GildedRoseTest.ApprovalTest.ThirtyDays.received.txt"
+
+    let fakeoutput = new StringBuilder()
+    Console.SetOut(new StringWriter(fakeoutput))
+    Console.SetIn(new StringReader("a\n"))
+
+    GildedRose.Program.main [||] |> ignore
+    let actual = fakeoutput.ToString()
+
+    Assert.Equal(expected, actual)