Write the first test

NightLight.Core.Tests/Arbitraries.fs

@@ -0,0 +1,22 @@
+namespace NightLight.Core.Tests
+
+open System
+open FsCheck.FSharp
+open NightLight.Core.Models
+
+type Arbitraries =
+    static member Interaction() =
+        let genTimeChangedInteraction =
+            gen {
+                let! time = ArbMap.defaults |> ArbMap.generate<DateTime>
+                return Interaction.TimeChanged time
+            }
+
+        let genHumanInteraction =
+            gen {
+                let! light = Gen.elements lights
+                let! humanInteraction = Gen.elements [ LightTurnedOn light; LightTurnedOff light ]
+                return Interaction.HumanInteraction humanInteraction
+            }
+
+        Gen.oneof [ genTimeChangedInteraction; genHumanInteraction ] |> Arb.fromGen