diff --git a/frontend/testing/unit/components/Sidebar.test.tsx b/frontend/testing/unit/components/Sidebar.test.tsx
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+++ b/frontend/testing/unit/components/Sidebar.test.tsx
@@ -0,0 +1,293 @@
+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { MemoryRouter } from 'react-router-dom';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import Sidebar from '../../../src/components/Sidebar';
+
+/* ------------------------------------------------------------------ */
+/*  Mocks                                                              */
+/* ------------------------------------------------------------------ */
+
+// Mock framer-motion to render plain elements so tests focus on behavior,
+// not animation internals.
+vi.mock('framer-motion', async () => {
+  const ReactModule = await import('react');
+  const createMotionProxy = () =>
+    new Proxy(
+      {},
+      {
+        get(_target: unknown, prop: string) {
+          return ReactModule.forwardRef((props: Record<string, unknown>, ref: React.Ref<unknown>) => {
+            // Strip framer-specific props so they don't leak to the DOM
+            const {
+              initial: _initial,
+              animate: _animate,
+              exit: _exit,
+              transition: _transition,
+              layoutId: _layoutId,
+              whileHover: _whileHover,
+              whileTap: _whileTap,
+              ...rest
+            } = props;
+            return ReactModule.createElement(prop, { ...rest, ref });
+          });
+        },
+      },
+    );
+
+  return {
+    motion: createMotionProxy(),
+    AnimatePresence: ({ children }: { children: React.ReactNode }) => <>{children}</>,
+  };
+});
+
+// Minimal ThemeToggle stub — the Sidebar imports it but its internals
+// are not under test here.
+vi.mock('../../../src/components/ThemeToggle', () => ({
+  default: () => <div data-testid="theme-toggle">ThemeToggle</div>,
+}));
+
+/* ------------------------------------------------------------------ */
+/*  Helpers                                                            */
+/* ------------------------------------------------------------------ */
+
+/**
+ * Renders the Sidebar inside a MemoryRouter so NavLink can resolve
+ * active state based on `initialRoute`.
+ */
+function renderSidebar(initialRoute = '/') {
+  return render(
+    <MemoryRouter initialEntries={[initialRoute]}>
+      <Sidebar />
+    </MemoryRouter>,
+  );
+}
+
+/* ------------------------------------------------------------------ */
+/*  Tests                                                              */
+/* ------------------------------------------------------------------ */
+
+describe('Sidebar', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    localStorage.clear();
+  });
+
+  /* ---------------------------------------------------------------
+   *  Collapse Persistence
+   * --------------------------------------------------------------- */
+  describe('collapse persistence', () => {
+    it('defaults to expanded when localStorage has no saved value', () => {
+      renderSidebar();
+
+      // All nav labels should be visible when expanded
+      expect(screen.getByText('Dashboard')).toBeInTheDocument();
+      expect(screen.getByText('Toolkit')).toBeInTheDocument();
+      expect(screen.getByText('Settings')).toBeInTheDocument();
+    });
+
+    it('restores collapsed state from localStorage', () => {
+      localStorage.setItem('sidebar-expanded', 'false');
+      renderSidebar();
+
+      // When collapsed the aside should have the narrow width style
+      const aside = document.querySelector('aside');
+      expect(aside).toBeInTheDocument();
+
+      // Labels should still render (AnimatePresence mock renders children),
+      // but the component reads the persisted value; verify localStorage was
+      // consumed correctly by checking that the toggle icon shows the
+      // "expand" arrow.
+      expect(
+        screen.getByText('keyboard_double_arrow_right'),
+      ).toBeInTheDocument();
+    });
+
+    it('restores expanded state from localStorage', () => {
+      localStorage.setItem('sidebar-expanded', 'true');
+      renderSidebar();
+
+      // Expanded state shows the "collapse" arrow
+      expect(
+        screen.getByText('keyboard_double_arrow_left'),
+      ).toBeInTheDocument();
+    });
+
+    it('persists collapsed state to localStorage after toggling', async () => {
+      const user = userEvent.setup();
+      renderSidebar();
+
+      // Initially expanded (default)
+      expect(localStorage.getItem('sidebar-expanded')).toBe('true');
+
+      // Click the sidebar to toggle collapse
+      await user.click(screen.getByRole('complementary'));
+
+      expect(localStorage.getItem('sidebar-expanded')).toBe('false');
+    });
+
+    it('persists expanded state when toggling back open', async () => {
+      const user = userEvent.setup();
+      localStorage.setItem('sidebar-expanded', 'false');
+      renderSidebar();
+
+      await user.click(screen.getByRole('complementary'));
+
+      expect(localStorage.getItem('sidebar-expanded')).toBe('true');
+    });
+
+    it('toggles via the dedicated toggle button', async () => {
+      const user = userEvent.setup();
+      renderSidebar();
+
+      await user.click(
+        screen.getByRole('button', { name: 'keyboard_double_arrow_left' }),
+      );
+
+      // After clicking the toggle button, the sidebar should be collapsed
+      expect(localStorage.getItem('sidebar-expanded')).toBe('false');
+      expect(
+        screen.getByText('keyboard_double_arrow_right'),
+      ).toBeInTheDocument();
+    });
+  });
+
+  /* ---------------------------------------------------------------
+   *  Active Nav State
+   * --------------------------------------------------------------- */
+  describe('active nav rendering', () => {
+    it('marks Dashboard link as active on "/"', () => {
+      renderSidebar('/');
+
+      const dashboardLink = screen.getByText('Dashboard').closest('a')!;
+      expect(dashboardLink).toHaveAttribute('href', '/');
+      expect(dashboardLink).toHaveAttribute('aria-current', 'page');
+    });
+
+    it('marks Toolkit link as active on "/toolkit"', () => {
+      renderSidebar('/toolkit');
+
+      const toolkitLink = screen.getByText('Toolkit').closest('a')!;
+      expect(toolkitLink).toHaveAttribute('href', '/toolkit');
+      expect(toolkitLink).toHaveAttribute('aria-current', 'page');
+    });
+
+    it('marks Settings link as active on "/settings"', () => {
+      renderSidebar('/settings');
+
+      const settingsLink = screen.getByText('Settings').closest('a')!;
+      expect(settingsLink).toHaveAttribute('href', '/settings');
+      expect(settingsLink).toHaveAttribute('aria-current', 'page');
+    });
+
+    it('marks Registry link as active on "/scans"', () => {
+      renderSidebar('/scans');
+
+      const scansLink = screen.getByText('Registry').closest('a')!;
+      expect(scansLink).toHaveAttribute('href', '/scans');
+      expect(scansLink).toHaveAttribute('aria-current', 'page');
+    });
+
+    it('does not mark non-active links with active styling', () => {
+      renderSidebar('/settings');
+
+      const dashboardLink = screen.getByText('Dashboard').closest('a')!;
+      expect(dashboardLink).not.toHaveAttribute('aria-current');
+    });
+
+    it('renders active indicator elements for the active link', () => {
+      renderSidebar('/');
+
+      const dashboardLink = screen.getByText('Dashboard').closest('a')!;
+      // The active link contains the glow div (layoutId="activeGlow") and
+      // the side bar div (layoutId="activeBar")
+      const glowDiv = dashboardLink.querySelector('[class*="bg-rag-red/5"]');
+      expect(glowDiv).toBeInTheDocument();
+    });
+
+    it('does not render active indicator elements for inactive links', () => {
+      renderSidebar('/settings');
+
+      const dashboardLink = screen.getByText('Dashboard').closest('a')!;
+      // Inactive link should NOT contain the active glow element
+      const glowDivs = dashboardLink.querySelectorAll('[class*="bg-rag-red/5"]');
+      expect(glowDivs.length).toBe(0);
+    });
+  });
+
+  /* ---------------------------------------------------------------
+   *  Highlighted Nav State
+   * --------------------------------------------------------------- */
+  describe('highlighted nav rendering', () => {
+    it('applies highlight styling to the Toolkit link when not active', () => {
+      // Navigate to a route that is NOT /toolkit so Toolkit is highlighted
+      // but not active
+      renderSidebar('/');
+
+      const toolkitLink = screen.getByText('Toolkit').closest('a')!;
+      expect(toolkitLink.className).toContain('bg-rag-blue/15');
+      expect(toolkitLink.className).toContain('border-rag-blue/30');
+    });
+
+    it('applies highlight icon styling to the Toolkit icon when not active', () => {
+      renderSidebar('/');
+
+      // The Toolkit icon should show the highlighted (blue) text
+      const toolkitIcon = screen.getByText('add_circle');
+      expect(toolkitIcon.className).toContain('text-rag-blue');
+    });
+
+    it('does not apply highlight styling to non-highlight links', () => {
+      renderSidebar('/');
+
+      // Dashboard is active here so skip it; check Findings which is
+      // neither active nor highlighted
+      const findingsLink = screen.getByText('Findings').closest('a')!;
+      expect(findingsLink.className).not.toContain('bg-rag-blue/15');
+    });
+
+    it('applies active styling instead of highlight when Toolkit is the active route', () => {
+      renderSidebar('/toolkit');
+
+      const toolkitLink = screen.getByText('Toolkit').closest('a')!;
+      expect(toolkitLink).toHaveAttribute('aria-current', 'page');
+      // Highlight-specific classes should NOT be present
+      expect(toolkitLink.className).not.toContain('bg-rag-blue/15');
+    });
+  });
+
+  /* ---------------------------------------------------------------
+   *  Nav Structure
+   * --------------------------------------------------------------- */
+  describe('navigation structure', () => {
+    it('renders all expected navigation links', () => {
+      renderSidebar();
+
+      const expectedLabels = [
+        'Toolkit',
+        'Dashboard',
+        'Registry',
+        'Findings',
+        'Reports',
+        'Workflows',
+        'Settings',
+      ];
+
+      for (const label of expectedLabels) {
+        expect(screen.getByText(label)).toBeInTheDocument();
+      }
+    });
+
+    it('renders section headers when expanded', () => {
+      renderSidebar();
+
+      expect(screen.getByText('Monitor')).toBeInTheDocument();
+      expect(screen.getByText('Analyze')).toBeInTheDocument();
+    });
+  });
+});