diff --git a/source/Trek-12/Tests/RulesTests.cs b/source/Trek-12/Tests/RulesTests.cs
index 56ec387..630cca2 100644
--- a/source/Trek-12/Tests/RulesTests.cs
+++ b/source/Trek-12/Tests/RulesTests.cs
@@ -232,4 +232,247 @@ public class RulesTests
         rules.IsZoneValidAndAddToZones(cell, map);
         Assert.Contains(cell, map.Zones[0]);
     }
+    
+    [Fact]
+    public void IsValueInZones_ReturnsFalse_WhenCellIsNull()
+    {
+        Rules rules = new Rules();
+        Assert.False(rules.IsValueInZones(null, new List<List<Cell>>()));
+    }
+
+    [Fact]
+    public void IsValueInZones_ReturnsFalse_WhenZonesAreEmpty()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        cell.Value = 1;
+        Assert.False(rules.IsValueInZones(cell, new List<List<Cell>>()));
+    }
+
+    [Fact]
+    public void IsValueInZones_ReturnsFalse_WhenNoZoneContainsCellWithSameValue()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        cell.Value = 1;
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { new Cell(0, 1) { Value = 2 } },
+            new List<Cell> { new Cell(1, 0) { Value = 3 } }
+        };
+        Assert.False(rules.IsValueInZones(cell, zones));
+    }
+
+    [Fact]
+    public void IsValueInZones_ReturnsTrue_WhenZoneContainsCellWithSameValue()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        cell.Value = 1;
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { new Cell(0, 1) { Value = 1 } },
+            new List<Cell> { new Cell(1, 0) { Value = 3 } }
+        };
+        Assert.True(rules.IsValueInZones(cell, zones));
+    }
+    
+    [Fact]
+    public void IsCellInZone_ReturnsFalse_WhenCellIsNull()
+    {
+        Rules rules = new Rules();
+        Assert.False(rules.IsCellInZone(null, new List<List<Cell>>()));
+    }
+
+    [Fact]
+    public void IsCellInZone_ReturnsFalse_WhenZonesAreEmpty()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        Assert.False(rules.IsCellInZone(cell, new List<List<Cell>>()));
+    }
+
+    [Fact]
+    public void IsCellInZone_ReturnsFalse_WhenNoZoneContainsCell()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { new Cell(0, 1) },
+            new List<Cell> { new Cell(1, 0) }
+        };
+        Assert.False(rules.IsCellInZone(cell, zones));
+    }
+
+    [Fact]
+    public void IsCellInZone_ReturnsTrue_WhenZoneContainsCell()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { new Cell(0, 1) },
+            new List<Cell> { cell }
+        };
+        Assert.True(rules.IsCellInZone(cell, zones));
+    }
+    
+    [Fact]
+    public void AddToZone_DoesNothing_WhenCellIsNull()
+    {
+        Rules rules = new Rules();
+        List<List<Cell>> zones = new List<List<Cell>>();
+        rules.AddToZone(null, zones);
+        Assert.Empty(zones);
+    }
+
+    [Fact]
+    public void AddToZone_DoesNothing_WhenCellValueIsNull()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        List<List<Cell>> zones = new List<List<Cell>>();
+        rules.AddToZone(cell, zones);
+        Assert.Empty(zones);
+    }
+
+    [Fact]
+    public void AddToZone_DoesNothing_WhenCellIsAlreadyInZone()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        cell.Value = 1;
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { cell }
+        };
+        rules.AddToZone(cell, zones);
+        Assert.Single(zones[0]); // Verify if the List has still only one element
+    }
+
+    [Fact]
+    public void AddToZone_AddsCellToExistingZone_WhenCellHasSameValueAsZone()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        cell.Value = 1;
+        List<List<Cell>> zones = new List<List<Cell>>
+        {
+            new List<Cell> { new Cell(0, 1) { Value = 1 } }
+        };
+        rules.AddToZone(cell, zones);
+        Assert.Contains(cell, zones[0]);
+    }
+    
+    [Fact]
+    public void NewZoneIsCreated_DoesNothing_WhenFirstCellIsNull()
+    {
+        Rules rules = new Rules();
+        Map map = new Map("background");
+        rules.NewZoneIsCreated(null, new Cell(0, 0), map);
+        Assert.Empty(map.Zones);
+    }
+
+    [Fact]
+    public void NewZoneIsCreated_DoesNothing_WhenSecondCellIsNull()
+    {
+        Rules rules = new Rules();
+        Map map = new Map("background");
+        rules.NewZoneIsCreated(new Cell(0, 0), null, map);
+        Assert.Empty(map.Zones);
+    }
+
+    [Fact]
+    public void NewZoneIsCreated_DoesNothing_WhenFirstCellValueIsNull()
+    {
+        Rules rules = new Rules();
+        Map map = new Map("background");
+        Cell firstCell = new Cell(0, 0);
+        rules.NewZoneIsCreated(firstCell, new Cell(0, 1), map);
+        Assert.Empty(map.Zones);
+    }
+
+    [Fact]
+    public void NewZoneIsCreated_DoesNothing_WhenSecondCellValueIsNull()
+    {
+        Rules rules = new Rules();
+        Map map = new Map("background");
+        Cell secondCell = new Cell(0, 0);
+        rules.NewZoneIsCreated(new Cell(0, 1), secondCell, map);
+        Assert.Empty(map.Zones);
+    }
+
+    [Fact]
+    public void NewZoneIsCreated_CreatesNewZone_WhenBothCellsAreNotNullAndHaveValues()
+    {
+        Rules rules = new Rules();
+        Map map = new Map("background");
+        Cell firstCell = new Cell(0, 0);
+        firstCell.Value = 1;
+        Cell secondCell = new Cell(0, 1);
+        secondCell.Value = 1;
+        rules.NewZoneIsCreated(firstCell, secondCell, map);
+        Assert.Single(map.Zones);
+        Assert.Contains(firstCell, map.Zones[0]);
+        Assert.Contains(secondCell, map.Zones[0]);
+    }
+    
+    [Fact]
+    public void EveryAdjacentCells_ReturnsEmptyList_WhenCellIsNull()
+    {
+        Rules rules = new Rules();
+        List<Cell> cells = new List<Cell> { new Cell(0, 0), new Cell(0, 1) };
+        Assert.Empty(rules.EveryAdjacentCells(null, cells));
+    }
+
+    [Fact]
+    public void EveryAdjacentCells_ReturnsEmptyList_WhenCellsAreEmpty()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        Assert.Empty(rules.EveryAdjacentCells(cell, new List<Cell>()));
+    }
+
+    [Fact]
+    public void EveryAdjacentCells_ReturnsEmptyList_WhenNoAdjacentCells()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        List<Cell> cells = new List<Cell> { new Cell(2, 2), new Cell(3, 3) };
+        Assert.Empty(rules.EveryAdjacentCells(cell, cells));
+    }
+
+    [Fact]
+    public void EveryAdjacentCells_ReturnsListWithAdjacentCells_WhenAdjacentCellsExist()
+    {
+        Rules rules = new Rules();
+        Cell cell = new Cell(0, 0);
+        List<Cell> cells = new List<Cell> { new Cell(0, 1), new Cell(1, 0), new Cell(2, 2) };
+        List<Cell> result = rules.EveryAdjacentCells(cell, cells);
+        Assert.Equal(2, result.Count);
+        Assert.Contains(new Cell(0, 1), result);
+        Assert.Contains(new Cell(1, 0), result);
+    }
+    
+    [Fact]
+    public void FinalCalculusOfZones_ReturnsZero_WhenZonesAreEmpty()
+    {
+        Rules rules = new Rules();
+        Assert.Equal(0, rules.FinalCalculusOfZones(new List<List<Cell>>()));
+    }
+
+    /*
+    [Fact]
+    public void FinalCalculusOfZones_ReturnsCorrectValue_WhenZonesAreNotEmpty()
+    {
+        // TODO
+    }
+    
+    [Fact]
+    public void FinalCalculusOfZones_ReturnsCorrectValue_WhenZoneCountIsGreaterThanNine()
+    {
+        // TODO
+    }
+    */
 }
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