Add timing tests for escaping JSON strings

On my machine, the escaped test case has a runtime of 74ms. The chosen range of up to 5000ms provides a wide range that precludes the pathological case while still being acheivable on underpowered hardware.

Tests should be converted to proper benchmarks in a later PR (see xyncro#70).

Also exposes internals to `Chiron.Tests`.

src/Chiron/Chiron.fs

@@ -1,4 +1,4 @@
-module Chiron
+module Chiron
 
 open System
 open System.Globalization
@@ -1130,3 +1130,6 @@ module Patterns =
             Optic.get (Json.Object_ >?> Map.key_ key)
          >> Option.bind (Json.tryDeserialize >> function | Choice1Of2 a -> Some a
                                                          | _ -> None)
+
+[<assembly:System.Runtime.CompilerServices.InternalsVisibleTo("Chiron.Tests")>]
+()

tests/Chiron.Tests/Chiron.Tests.fs

@@ -124,6 +124,28 @@ let ``Json.format returns correct values`` () =
     Json.format (String "푟") =! "\"푟\""
     Json.format (String "\t") =! "\"\\t\""
 
+[<Fact>]
+let ``escape is not pathological for cases with escapes`` () =
+    let testObj =
+        Json.Array
+            [ for i in 1..100000 do
+                yield Json.String <| "he\nllo\u0006\t 푟 " + string i ]
+    let testString = Json.format testObj
+    let sw = System.Diagnostics.Stopwatch.StartNew()
+    let escaped = Escaping.escape testString
+    let time = sw.ElapsedMilliseconds
+    printfn "String length: %i, JSON escaped length: %i, Time: %i ms" (String.length testString) (String.length escaped) time
+    Assert.InRange(time, 0L, 5000L)
+
+[<Fact>]
+let ``escape is not pathological for non-escaped cases`` () =
+    let testString = String.replicate 2500000 "a"
+    let sw = System.Diagnostics.Stopwatch.StartNew()
+    let escaped = Escaping.escape testString
+    let time = sw.ElapsedMilliseconds
+    printfn "String length: %i, JSON escaped length: %i, Time: %i ms" (String.length testString) (String.length escaped) time
+    Assert.InRange(time, 0L, 5000L)
+
 (* Mapping
 
    Tests exercising mapping functions between Json and other F#