add a sleep period when creating an overlay in library tests.

TestCentre/LibraryTests.fs

@@ -2,7 +2,6 @@
 
     module PropertyTests =
 
-        open Xunit
         open FsCheck.Xunit
         open System
         open System.Drawing
@@ -10,6 +9,7 @@
         open System.Reflection
         open SmoulderingBeachBall.Services
         open System.IO
+        open System.Threading
 
         (* '3000' is an arbitary value. It is used to keep the testing times sane.
         This function is used to randomly generate image sizes but you do not need to use it.
@@ -51,8 +51,18 @@
                 files
                 |> Array.iter (fun f -> File.Delete(f))
 
+        let buildBorderOverlay () =
+            Thread.Sleep 100 // Helps generate better colour variation.
+            { colour = randomColour () :?> Brush
+              overlayType = Border }
+
+        let buildFullOverlay () =
+            Thread.Sleep 100 // Helps generate better colour variation.
+            { colour = randomColour () :?> Brush
+              overlayType = Full }
+
         [<Property>]
-        let ``can create an image with no overlay`` () =
+        let ``Can create an image with no overlay`` () =
             resetSavingTestArea ()
             let spec =
                 { // See note accompanying 'randomInt' function for constraints information.
@@ -63,3 +73,16 @@
                   overlay = None }
             makeImage spec |> Async.RunSynchronously
             fileSaved (spec.width.ToString()) (spec.height.ToString()) = true
+
+        [<Property>]
+        let ``Can create image with border`` () =
+            resetSavingTestArea ()
+            let spec =
+                { // See note accompanying 'randomInt' function for constraints information.
+                  width =  randomInt ()
+                  height = randomInt ()
+                  colour = randomColour () :?> Brush
+                  filePath = saveLocation
+                  overlay = Some (buildBorderOverlay ()) }
+            makeImage spec |> Async.RunSynchronously
+            fileSaved (spec.width.ToString()) (spec.height.ToString()) = true