diff --git a/NightLight.Core.Tests/Arbitraries.fs b/NightLight.Core.Tests/Arbitraries.fs
deleted file mode 100644
index 379c39e..0000000
--- a/NightLight.Core.Tests/Arbitraries.fs
+++ /dev/null
@@ -1,29 +0,0 @@
-namespace NightLight.Core.Tests
-
-open System
-open FsCheck
-open FsCheck.FSharp
-open NightLight.Core.Models
-
-type Arbitraries =
-    static member Interactions() : Arbitrary<Interaction list> =
-        gen {
-            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
-                }
-
-            let! initialTimeChangedInteraction = genTimeChangedInteraction
-            let! remainingInteractions = Gen.oneof [ genTimeChangedInteraction; genHumanInteraction ] |> Gen.listOf
-
-            return initialTimeChangedInteraction :: remainingInteractions
-        }
-        |> Arb.fromGen
diff --git a/NightLight.Core.Tests/ArbitraryInteractionLists.fs b/NightLight.Core.Tests/ArbitraryInteractionLists.fs
new file mode 100644
index 0000000..9098db1
--- /dev/null
+++ b/NightLight.Core.Tests/ArbitraryInteractionLists.fs
@@ -0,0 +1,25 @@
+module NightLight.Core.Tests.ArbitraryInteractionLists
+
+open System
+open FsCheck.FSharp
+open NightLight.Core.Tests.InteractionListGenerators
+
+let private isDay (time: DateTime) =
+    time.TimeOfDay >= TimeSpan.FromHours 5.5
+    && time.TimeOfDay < TimeSpan.FromHours 20.5
+
+type ArbitraryInteractionsListThatEndsDuringTheDay =
+    static member InteractionsList() =
+        ArbMap.defaults
+        |> ArbMap.generate<DateTime>
+        |> Gen.filter isDay
+        |> Gen.bind genInteractionsListThatEndsAtTime
+        |> Arb.fromGen
+
+type ArbitraryInteractionsListThatEndsDuringTheNight =
+    static member InteractionsList() =
+        ArbMap.defaults
+        |> ArbMap.generate<DateTime>
+        |> Gen.filter (not << isDay)
+        |> Gen.bind genInteractionsListThatEndsAtTime
+        |> Arb.fromGen
diff --git a/NightLight.Core.Tests/InteractionListGenerators.fs b/NightLight.Core.Tests/InteractionListGenerators.fs
new file mode 100644
index 0000000..d1e1925
--- /dev/null
+++ b/NightLight.Core.Tests/InteractionListGenerators.fs
@@ -0,0 +1,41 @@
+module NightLight.Core.Tests.InteractionListGenerators
+
+open System
+open FsCheck.FSharp
+open NightLight.Core.Models
+
+let private genTimeChangedInteraction =
+    ArbMap.defaults |> ArbMap.generate<DateTime> |> Gen.map Interaction.TimeChanged
+
+let private genHumanInteraction =
+    Gen.elements lights
+    |> Gen.bind (fun light ->
+        [ LightTurnedOn light; LightTurnedOff light ]
+        |> Gen.elements
+        |> Gen.map Interaction.HumanInteraction)
+
+let private genInteraction =
+    Gen.oneof [ genTimeChangedInteraction; genHumanInteraction ]
+
+let private genInteractionsListThatStartsWithTimeChange =
+    gen {
+        let! firstInteraction = genTimeChangedInteraction
+        let! remainingInteractions = Gen.listOf genInteraction
+        return firstInteraction :: remainingInteractions
+    }
+
+let private genInteractionsListWhere condition =
+    Gen.listOf (genInteraction |> Gen.filter condition)
+
+let genInteractionsListThatEndsAtTime time =
+    let genTrivialList = Gen.constant <| List.singleton (Interaction.TimeChanged time)
+
+    let genNonTrivialList =
+        gen {
+            let! before = genInteractionsListThatStartsWithTimeChange
+            let interactionThatSetsEndTime = Interaction.TimeChanged time
+            let! after = genInteractionsListWhere (not << _.IsTimeChanged)
+            return before @ interactionThatSetsEndTime :: after
+        }
+
+    Gen.frequency [ 1, genTrivialList; 9, genNonTrivialList ]
diff --git a/NightLight.Core.Tests/NightLight.Core.Tests.fsproj b/NightLight.Core.Tests/NightLight.Core.Tests.fsproj
index 5d37e21..66f25e0 100644
--- a/NightLight.Core.Tests/NightLight.Core.Tests.fsproj
+++ b/NightLight.Core.Tests/NightLight.Core.Tests.fsproj
@@ -8,7 +8,8 @@
 
     <ItemGroup>
         <Compile Include="FakeHome.fs" />
-        <Compile Include="Arbitraries.fs" />
+        <Compile Include="InteractionListGenerators.fs" />
+        <Compile Include="ArbitraryInteractionLists.fs" />
         <Compile Include="NightLightTests.fs" />
     </ItemGroup>
 
diff --git a/NightLight.Core.Tests/NightLightTests.fs b/NightLight.Core.Tests/NightLightTests.fs
index d33631c..0402695 100644
--- a/NightLight.Core.Tests/NightLightTests.fs
+++ b/NightLight.Core.Tests/NightLightTests.fs
@@ -1,31 +1,9 @@
 namespace NightLight.Core.Tests
 
-open System
 open NightLight.Core.Core
+open NightLight.Core.Tests.ArbitraryInteractionLists
 open FsCheck.Xunit
-open FsCheck.FSharp
 
-module InteractionsHelpers =
-    let getTimeAfter interactions =
-        interactions
-        |> Seq.choose (fun interaction ->
-            match interaction with
-            | TimeChanged time -> Some time
-            | _ -> None)
-        |> Seq.tryLast
-        |> function
-            | Some time -> time
-            | None -> failwith "Time wasn't changed"
-
-    let isDayAfter interactions =
-        let time = getTimeAfter interactions
-
-        time.TimeOfDay >= TimeSpan.FromHours 5.5
-        && time.TimeOfDay < TimeSpan.FromHours 20.5
-
-    let isNightAfter = not << isDayAfter
-
-[<Properties(Arbitrary = [| typeof<Arbitraries> |])>]
 type NightLightTests() =
     let createFakeHomeWithNightLightAndInteract (interactions: Interaction list) =
         let mutable nightLightStateMachine = NightLightStateMachine()
@@ -43,16 +21,12 @@ type NightLightTests() =
 
         fakeHome
 
-    [<Property>]
+    [<Property(Arbitrary = [| typeof<ArbitraryInteractionsListThatEndsDuringTheNight> |])>]
     let ``Lights should be red during the night`` (interactions: Interaction list) =
         let fakeHome = createFakeHomeWithNightLightAndInteract interactions
+        fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = Red)
 
-        InteractionsHelpers.isNightAfter interactions
-        ==> fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = Red)
-
-    [<Property>]
+    [<Property(Arbitrary = [| typeof<ArbitraryInteractionsListThatEndsDuringTheDay> |])>]
     let ``Lights should be white or yellow during the day`` (interactions: Interaction list) =
         let fakeHome = createFakeHomeWithNightLightAndInteract interactions
-
-        InteractionsHelpers.isDayAfter interactions
-        ==> fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = White || color = Yellow)
+        fakeHome.ForAllLightsThatAreOn(fun (_, _, color) -> color = White || color = Yellow)