Add comprehensive tests for effective cost calculations in ViewModels

Co-authored-by: LeftofZen <7483209+LeftofZen@users.noreply.github.com>

Author: Copilot

Tests/EffectiveCostTests.cs

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+using Definitions.ObjectModels.Objects.Track;
+using Definitions.ObjectModels.Objects.Bridge;
+using Gui;
+using Gui.ViewModels;
+using NUnit.Framework;
+
+namespace Gui.Tests;
+
+[TestFixture]
+public class EffectiveCostTests
+{
+	[SetUp]
+	public void Setup()
+	{
+		// Set up global settings
+		GlobalSettings.CurrentSettings = new EditorSettings
+		{
+			InflationYear = 1950
+		};
+	}
+
+	[Test]
+	public void TrackViewModel_CalculatesEffectiveCosts()
+	{
+		var trackObject = new TrackObject
+		{
+			BuildCostFactor = 100,
+			SellCostFactor = -50,
+			TunnelCostFactor = 200,
+			CostIndex = 0
+		};
+
+		var viewModel = new TrackViewModel(trackObject);
+
+		// For year 1950, with factor 1024 and divisor 10, we should get: (100 * X) / 1024
+		// where X is the inflation-adjusted currency multiplication factor
+		Assert.That(viewModel.EffectiveBuildCost, Is.GreaterThan(0));
+		Assert.That(viewModel.EffectiveSellCost, Is.LessThan(0));
+		Assert.That(viewModel.EffectiveTunnelCost, Is.GreaterThan(0));
+		
+		// Build cost should be proportional to the factors
+		Assert.That(viewModel.EffectiveTunnelCost, Is.GreaterThan(viewModel.EffectiveBuildCost));
+	}
+
+	[Test]
+	public void BridgeViewModel_CalculatesEffectiveCosts()
+	{
+		var bridgeObject = new BridgeObject
+		{
+			BaseCostFactor = 150,
+			HeightCostFactor = 50,
+			SellCostFactor = -75,
+			CostIndex = 1
+		};
+
+		var viewModel = new BridgeViewModel(bridgeObject);
+
+		Assert.That(viewModel.EffectiveBaseCost, Is.GreaterThan(0));
+		Assert.That(viewModel.EffectiveHeightCost, Is.GreaterThan(0));
+		Assert.That(viewModel.EffectiveSellCost, Is.LessThan(0));
+		
+		// Base cost should be greater than height cost
+		Assert.That(viewModel.EffectiveBaseCost, Is.GreaterThan(viewModel.EffectiveHeightCost));
+	}
+
+	[Test]
+	public void InflationYear_AffectsCosts()
+	{
+		var trackObject = new TrackObject
+		{
+			BuildCostFactor = 100,
+			CostIndex = 0
+		};
+
+		// Test with year 1900 (no inflation)
+		GlobalSettings.CurrentSettings!.InflationYear = 1900;
+		var viewModel1900 = new TrackViewModel(trackObject);
+		var cost1900 = viewModel1900.EffectiveBuildCost;
+
+		// Test with year 2000 (with inflation)
+		GlobalSettings.CurrentSettings!.InflationYear = 2000;
+		var viewModel2000 = new TrackViewModel(trackObject);
+		var cost2000 = viewModel2000.EffectiveBuildCost;
+
+		// Cost in 2000 should be higher due to inflation
+		Assert.That(cost2000, Is.GreaterThan(cost1900));
+	}
+
+	[Test]
+	public void GlobalSettings_DefaultYear_WorksCorrectly()
+	{
+		// Test that if GlobalSettings is null, default year is used
+		GlobalSettings.CurrentSettings = null;
+
+		var trackObject = new TrackObject
+		{
+			BuildCostFactor = 100,
+			CostIndex = 0
+		};
+
+		var viewModel = new TrackViewModel(trackObject);
+		
+		// Should not throw and should return a valid cost
+		Assert.That(viewModel.EffectiveBuildCost, Is.GreaterThan(0));
+	}
+}