test(09-04): add StorageViewModel chart unit tests

- 7 tests covering chart series from metrics, bar series structure,
  donut/bar toggle, top-10+Other aggregation, no-Other for <=10,
  tenant switch cleanup, and empty data handling
- Added LiveChartsCore.SkiaSharpView.WPF to test project
- Uses reflection to set FileTypeMetrics (private setter) directly

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SharepointToolbox.Tests/ViewModels/StorageViewModelChartTests.cs

@@ -0,0 +1,217 @@
+using System.Collections.ObjectModel;
+using System.Reflection;
+using CommunityToolkit.Mvvm.Messaging;
+using LiveChartsCore;
+using LiveChartsCore.SkiaSharpView;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using SharepointToolbox.Core.Messages;
+using SharepointToolbox.Core.Models;
+using SharepointToolbox.Services;
+using SharepointToolbox.ViewModels;
+using SharepointToolbox.ViewModels.Tabs;
+
+namespace SharepointToolbox.Tests.ViewModels;
+
+/// <summary>
+/// Unit tests for StorageViewModel chart functionality (Phase 09 Plan 04).
+/// Verifies: chart series from metrics, bar series structure, donut/bar toggle,
+/// top-10 + Other aggregation, no-Other for <=10, tenant switch cleanup, empty data.
+/// Uses reflection to set FileTypeMetrics directly, bypassing ClientContext dependency.
+/// </summary>
+public class StorageViewModelChartTests
+{
+    public StorageViewModelChartTests()
+    {
+        WeakReferenceMessenger.Default.Reset();
+    }
+
+    // -- Helper factories --------------------------------------------------------
+
+    private static StorageViewModel CreateViewModel()
+    {
+        var mockStorage = new Mock<IStorageService>();
+        var mockSession = new Mock<ISessionManager>();
+
+        var vm = new StorageViewModel(
+            mockStorage.Object,
+            mockSession.Object,
+            NullLogger<FeatureViewModelBase>.Instance);
+
+        vm.SetCurrentProfile(new TenantProfile
+        {
+            Name = "Test",
+            TenantUrl = "https://test.sharepoint.com",
+            ClientId = "test-id"
+        });
+
+        return vm;
+    }
+
+    /// <summary>
+    /// Sets FileTypeMetrics via the property (private setter) using reflection,
+    /// which also triggers UpdateChartSeries.
+    /// </summary>
+    private static void SetFileTypeMetrics(StorageViewModel vm, IList<FileTypeMetric> metrics)
+    {
+        var prop = typeof(StorageViewModel).GetProperty(
+            nameof(StorageViewModel.FileTypeMetrics),
+            BindingFlags.Public | BindingFlags.Instance);
+        prop!.SetValue(vm, new ObservableCollection<FileTypeMetric>(metrics));
+    }
+
+    private static List<FileTypeMetric> MakeMetrics(int count)
+    {
+        var extensions = new[]
+        {
+            ".docx", ".pdf", ".xlsx", ".pptx", ".jpg",
+            ".png", ".mp4", ".zip", ".csv", ".html",
+            ".txt", ".json", ".xml", ".msg", ".eml"
+        };
+
+        var metrics = new List<FileTypeMetric>();
+        for (int i = 0; i < count; i++)
+        {
+            string ext = i < extensions.Length ? extensions[i] : $".ext{i}";
+            metrics.Add(new FileTypeMetric(ext, (count - i) * 1024L * 1024, (count - i) * 10));
+        }
+        return metrics;
+    }
+
+    // -- Test 1: Chart series populated from metrics -----------------------------
+
+    [Fact]
+    public void After_setting_metrics_HasChartData_is_true_and_PieChartSeries_has_entries()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(5);
+
+        SetFileTypeMetrics(vm, metrics);
+
+        Assert.True(vm.HasChartData);
+        Assert.NotEmpty(vm.PieChartSeries);
+        Assert.Equal(5, vm.PieChartSeries.Count());
+    }
+
+    // -- Test 2: Bar series has one ColumnSeries with correct value count --------
+
+    [Fact]
+    public void After_setting_metrics_BarChartSeries_has_one_ColumnSeries_with_matching_values()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(5);
+
+        SetFileTypeMetrics(vm, metrics);
+
+        var barSeries = vm.BarChartSeries.ToList();
+        Assert.Single(barSeries);
+
+        var columnSeries = Assert.IsType<ColumnSeries<long>>(barSeries[0]);
+        Assert.Equal(5, columnSeries.Values!.Count());
+    }
+
+    // -- Test 3: Toggle IsDonutChart changes PieChartSeries InnerRadius ----------
+
+    [Fact]
+    public void Toggle_IsDonutChart_changes_PieChartSeries_InnerRadius()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(3);
+
+        SetFileTypeMetrics(vm, metrics);
+
+        // Initially IsDonutChart=true => InnerRadius=50
+        var pieBefore = vm.PieChartSeries.Cast<PieSeries<long>>().ToList();
+        Assert.All(pieBefore, s => Assert.Equal(50, s.InnerRadius));
+
+        // Toggle to bar (not donut) => InnerRadius=0
+        vm.IsDonutChart = false;
+
+        var pieAfter = vm.PieChartSeries.Cast<PieSeries<long>>().ToList();
+        Assert.All(pieAfter, s => Assert.Equal(0, s.InnerRadius));
+    }
+
+    // -- Test 4: More than 10 file types => 11 entries (10 + Other) --------------
+
+    [Fact]
+    public void More_than_10_metrics_produces_11_series_entries_with_Other()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(15);
+
+        SetFileTypeMetrics(vm, metrics);
+
+        // Pie series: 10 real + 1 "Other" = 11
+        Assert.Equal(11, vm.PieChartSeries.Count());
+
+        // Last pie entry should be named "OTHER" (DisplayLabel uppercases extension)
+        var lastPie = vm.PieChartSeries.Last();
+        Assert.Equal("OTHER", lastPie.Name);
+
+        // Bar series column should have 11 values
+        var columnSeries = Assert.IsType<ColumnSeries<long>>(vm.BarChartSeries.First());
+        Assert.Equal(11, columnSeries.Values!.Count());
+
+        // X-axis should have 11 labels
+        Assert.Equal(11, vm.BarXAxes[0].Labels!.Count);
+    }
+
+    // -- Test 5: 10 or fewer file types => no "Other" entry ----------------------
+
+    [Fact]
+    public void Ten_or_fewer_metrics_produces_no_Other_entry()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(10);
+
+        SetFileTypeMetrics(vm, metrics);
+
+        Assert.Equal(10, vm.PieChartSeries.Count());
+
+        // No entry named "OTHER" (DisplayLabel uppercases)
+        Assert.DoesNotContain(vm.PieChartSeries, s => s.Name == "OTHER");
+    }
+
+    // -- Test 6: Tenant switch clears chart data ---------------------------------
+
+    [Fact]
+    public void OnTenantSwitched_clears_FileTypeMetrics_and_HasChartData_is_false()
+    {
+        var vm = CreateViewModel();
+        var metrics = MakeMetrics(5);
+
+        SetFileTypeMetrics(vm, metrics);
+        Assert.True(vm.HasChartData);
+
+        // Act: send TenantSwitchedMessage
+        var newProfile = new TenantProfile
+        {
+            Name = "NewTenant",
+            TenantUrl = "https://newtenant.sharepoint.com",
+            ClientId = "new-id"
+        };
+        WeakReferenceMessenger.Default.Send(new TenantSwitchedMessage(newProfile));
+
+        Assert.False(vm.HasChartData);
+        Assert.Empty(vm.FileTypeMetrics);
+        Assert.Empty(vm.PieChartSeries);
+        Assert.Empty(vm.BarChartSeries);
+    }
+
+    // -- Test 7: Empty metrics => HasChartData false, series empty ---------------
+
+    [Fact]
+    public void Empty_metrics_yields_HasChartData_false_and_empty_series()
+    {
+        var vm = CreateViewModel();
+
+        SetFileTypeMetrics(vm, new List<FileTypeMetric>());
+
+        Assert.False(vm.HasChartData);
+        Assert.Empty(vm.PieChartSeries);
+        Assert.Empty(vm.BarChartSeries);
+        Assert.Empty(vm.BarXAxes);
+        Assert.Empty(vm.BarYAxes);
+    }
+}