diff --git a/ACCESSIBILITY_IMPROVEMENTS.md b/ACCESSIBILITY_IMPROVEMENTS.md
new file mode 100644
index 0000000..592a795
--- /dev/null
+++ b/ACCESSIBILITY_IMPROVEMENTS.md
@@ -0,0 +1,357 @@
+# Accessibility & Testing Improvements
+
+## Overview
+This document summarizes all accessibility enhancements and data-testid attributes added to the CodeSnippet application. These improvements make the application more accessible to screen reader users and easier to test programmatically.
+
+---
+
+## Navigation Components
+
+### Navigation.tsx
+- **Added:** `aria-expanded` - Indicates navigation menu state
+- **Added:** `aria-controls="navigation-sidebar"` - Links button to controlled element
+- **Added:** `data-testid="navigation-toggle-btn"` - Test identifier for menu toggle
+- **Added:** `aria-hidden="true"` to icon - Hides decorative icon from screen readers
+
+### NavigationSidebar.tsx
+✅ **Already had:** `data-testid` attributes on overlay and sidebar
+- **Added:** `id="navigation-sidebar"` - Enables aria-controls reference
+- **Added:** `role="navigation"` - Explicit semantic role
+- **Added:** `aria-label="Main navigation menu"` - Descriptive label
+- **Navigation items:** `data-testid={`nav-link-${item.path.replace(/\//g, '-')}`}` for dynamic test IDs
+- **Sidebar close button:** `data-testid="navigation-sidebar-close-btn"`
+
+### PageLayout.tsx
+- **Added:** `data-testid="page-layout"` to main container
+- **Added:** `data-testid="page-header"` to header element
+- **Added:** `data-testid="logo-text"` to logo
+- **Added:** `data-testid="main-content"` to main element
+- **Added:** `aria-hidden="true"` to decorative grid-pattern
+
+---
+
+## Snippet Manager Components
+
+### SnippetManagerRedux.tsx
+- **Added:** `data-testid="snippet-manager"` to main container
+- **Added:** `data-testid="snippet-manager-loading"` to loading state
+
+### SnippetToolbar.tsx
+✅ **Already had:** Comprehensive data-testid and aria attributes
+- **Enhanced:** Added `data-testid` for template menu items:
+  - `snippet-template-react-${template.id}`
+  - `snippet-template-python-${template.id}`
+  - `snippet-template-javascript-${template.id}`
+- **Already present:**
+  - `data-testid="snippet-search-input"` with `aria-label`
+  - `data-testid="snippet-selection-mode-btn"` with `aria-pressed`
+  - `data-testid="snippet-create-menu-trigger"`
+
+### SnippetCard.tsx
+✅ **Already had:** `data-testid={`snippet-card-${snippet.id}`}` and `role="article"`
+
+### SnippetCardActions.tsx
+✅ **Already had:** Comprehensive data-testid attributes:
+- `snippet-card-view-btn`
+- `snippet-card-copy-btn`
+- `snippet-card-edit-btn`
+- `snippet-card-actions-menu` (three-dot menu)
+- `snippet-card-move-submenu`
+- `move-to-namespace-${namespace.id}`
+- `snippet-card-delete-btn`
+- All buttons have appropriate `aria-label` attributes
+
+### SelectionControls.tsx
+- **Added:** `data-testid="selection-controls"` to main container
+- **Added:** `data-testid="select-all-btn"` with `aria-label`
+- **Added:** `data-testid="selection-count"` to count display
+- **Added:** `data-testid="bulk-move-menu-trigger"` with `aria-label`
+- **Added:** `data-testid="bulk-move-menu"` to menu container
+- **Added:** `data-testid={`bulk-move-to-namespace-${namespace.id}`}` for menu items
+- **Added:** `aria-hidden="true"` to folder icon
+
+### SnippetGrid.tsx
+✅ **Already had:** `data-testid="snippet-grid"` with `role="region"` and `aria-label`
+
+### NamespaceSelector.tsx
+✅ **Already had:** Comprehensive data-testid:
+- `namespace-selector-trigger`
+- `namespace-selector-content`
+- `namespace-option-${namespace.id}`
+
+---
+
+## Form Components
+
+### SnippetFormFields.tsx
+✅ **Already had:** Excellent accessibility implementation:
+- **Title input:**
+  - `data-testid="snippet-title-input"`
+  - `aria-invalid={!!errors.title}`
+  - `aria-describedby="title-error"` (when error present)
+- **Language select:**
+  - `data-testid="snippet-language-select"` with `aria-label`
+  - `data-testid="snippet-language-options"` on content
+  - `data-testid={`language-option-${lang}`}` on items
+- **Description textarea:**
+  - `data-testid="snippet-description-textarea"`
+  - `aria-label="Snippet description"`
+
+### SnippetDialog.tsx
+✅ **Already had:**
+- `data-testid="snippet-dialog"` on DialogContent
+- `data-testid="snippet-dialog-cancel-btn"`
+- `data-testid="snippet-dialog-save-btn"`
+
+### SnippetViewer.tsx
+- **Added:** `data-testid="snippet-viewer-dialog"` on DialogContent
+
+### SnippetViewerHeader.tsx
+- **Added:** `data-testid="snippet-viewer-toggle-preview-btn"` with `aria-pressed` and `aria-label`
+- **Added:** `data-testid="snippet-viewer-copy-btn"` with descriptive `aria-label`
+- **Added:** `data-testid="snippet-viewer-edit-btn"` with `aria-label`
+- **Added:** `aria-hidden="true"` to all icons
+
+---
+
+## UI Primitive Components
+
+### button.tsx
+✅ **Passes through all props** - Supports data-testid and accessibility attributes
+
+### input.tsx
+✅ **Passes through all props** - Supports data-testid and accessibility attributes
+
+### dialog.tsx
+- **DialogOverlay:**
+  - **Added:** `aria-hidden="true"` - Hides scrim from accessibility tree
+  - **Added:** `data-testid="dialog-overlay"` - Test identifier
+- **DialogContent close button:**
+  - **Enhanced:** `aria-label="Close dialog"` (more descriptive)
+  - **Added:** `data-testid="dialog-close-btn"`
+
+### sonner.tsx (Toast component)
+- **Added:** `data-testid="toast-container"` to Toaster component
+- **Added:** `position="bottom-right"` for consistent positioning
+- ✅ Sonner library automatically manages `aria-live` and `role="status"` on toast notifications
+
+---
+
+## Accessibility Patterns Implemented
+
+### ARIA Attributes
+| Attribute | Component | Purpose |
+|-----------|-----------|---------|
+| `aria-label` | Multiple | Provides accessible name for buttons and regions |
+| `aria-expanded` | Navigation toggle | Indicates menu open/closed state |
+| `aria-pressed` | Toggle buttons | Indicates pressed state for toggles |
+| `aria-hidden` | Decorative elements | Hides non-semantic elements from screen readers |
+| `aria-controls` | Navigation button | Links trigger to controlled element |
+| `aria-modal` | Dialog | Marks dialog as modal |
+| `role="dialog"` | Dialog container | Semantic dialog role |
+| `aria-describedby` | Form inputs | Links errors to input fields |
+| `aria-invalid` | Form inputs | Marks invalid form fields |
+| `aria-label` | Regions | Descriptive labels for landmark regions |
+
+### Semantic HTML
+- ✅ `<nav>` - Navigation sections
+- ✅ `<main>` - Main content area
+- ✅ `<header>` - Page header
+- ✅ `<footer>` - Page footer
+- ✅ `<aside>` - Sidebar (if present)
+- ✅ `<article>` - Snippet cards
+- ✅ `role="region"` - Content grids
+
+---
+
+## Testing Identifiers (data-testid)
+
+### Navigation
+```
+- navigation-toggle-btn
+- navigation-sidebar
+- navigation-sidebar-overlay
+- navigation-sidebar-close-btn
+- navigation-items
+- nav-link-{path}
+```
+
+### Layout
+```
+- page-layout
+- page-header
+- logo-text
+- main-content
+- dialog-overlay
+- dialog-close-btn
+```
+
+### Snippet Manager
+```
+- snippet-manager
+- snippet-manager-loading
+- snippet-search-input
+- snippet-selection-mode-btn
+- snippet-create-menu-trigger
+- snippet-template-react-{id}
+- snippet-template-python-{id}
+- snippet-template-javascript-{id}
+- snippet-card-{id}
+- snippet-grid
+```
+
+### Snippet Actions
+```
+- snippet-card-view-btn
+- snippet-card-copy-btn
+- snippet-card-edit-btn
+- snippet-card-actions-menu
+- snippet-card-move-submenu
+- move-to-namespace-{id}
+- snippet-card-delete-btn
+```
+
+### Selection & Bulk Operations
+```
+- selection-controls
+- select-all-btn
+- selection-count
+- bulk-move-menu-trigger
+- bulk-move-menu
+- bulk-move-to-namespace-{id}
+```
+
+### Forms
+```
+- snippet-title-input
+- snippet-language-select
+- snippet-language-options
+- language-option-{lang}
+- snippet-description-textarea
+- snippet-dialog
+- snippet-dialog-cancel-btn
+- snippet-dialog-save-btn
+```
+
+### Snippet Viewer
+```
+- snippet-viewer-dialog
+- snippet-viewer-toggle-preview-btn
+- snippet-viewer-copy-btn
+- snippet-viewer-edit-btn
+```
+
+### Namespaces
+```
+- namespace-selector-trigger
+- namespace-selector-content
+- namespace-option-{id}
+```
+
+### Toasts
+```
+- toast-container
+```
+
+---
+
+## Best Practices Applied
+
+### 1. **Icon Accessibility**
+- All decorative icons have `aria-hidden="true"`
+- Icon buttons always have `aria-label` or contextual button text
+
+### 2. **Form Accessibility**
+- Error messages linked via `aria-describedby`
+- Invalid fields marked with `aria-invalid="true"`
+- Labels properly associated with inputs via `htmlFor`
+
+### 3. **Interactive Elements**
+- Buttons have descriptive labels
+- Toggle buttons use `aria-pressed` for state
+- Dropdowns have clear trigger labels
+
+### 4. **Screen Reader Support**
+- All interactive regions have `aria-label` or `aria-labelledby`
+- Decorative elements properly hidden
+- Loading states announced with text
+- Status messages using Sonner's built-in `aria-live="polite"`
+
+### 5. **Testing Support**
+- Semantic data-testid naming convention
+- IDs include context (e.g., `snippet-card-{id}`)
+- Dynamic IDs parameterized for consistency
+
+---
+
+## Testing Usage Examples
+
+### Selecting Elements in Tests
+```typescript
+// Navigation
+cy.get('[data-testid="navigation-toggle-btn"]').click()
+cy.get('[data-testid="navigation-sidebar"]').should('be.visible')
+
+// Snippet Management
+cy.get('[data-testid="snippet-search-input"]').type('react')
+cy.get('[data-testid="snippet-card-abc123"]').click()
+cy.get('[data-testid="snippet-card-copy-btn"]').click()
+
+// Forms
+cy.get('[data-testid="snippet-title-input"]').type('New Snippet')
+cy.get('[data-testid="snippet-dialog-save-btn"]').click()
+
+// Selection
+cy.get('[data-testid="select-all-btn"]').click()
+cy.get('[data-testid="bulk-move-menu-trigger"]').click()
+```
+
+---
+
+## Accessibility Testing Checklist
+
+### Screen Reader Testing
+- [ ] Test with NVDA (Windows) or JAWS
+- [ ] Test with VoiceOver (macOS)
+- [ ] Verify all buttons have descriptive labels
+- [ ] Verify form errors are announced
+
+### Keyboard Navigation
+- [ ] All interactive elements are keyboard accessible
+- [ ] Tab order is logical (automatic with semantic HTML)
+- [ ] Modal dialogs trap focus
+- [ ] Escape key closes modals
+
+### Visual Accessibility
+- [ ] Sufficient color contrast (WCAG AA minimum)
+- [ ] Focus indicators are visible
+- [ ] Text is resizable
+- [ ] No information conveyed by color alone
+
+### Automated Testing
+- [ ] Use `data-testid` for E2E tests
+- [ ] Run axe-core or similar for automated checks
+- [ ] Test responsive design with screen readers
+
+---
+
+## Future Enhancements
+
+1. **Add keyboard shortcuts** - Document and implement vim-style shortcuts
+2. **Enhanced tooltips** - Add aria-describedby tooltips for complex UI
+3. **Loading states** - Add aria-busy for async operations
+4. **Pagination** - Add aria-label for pagination controls
+5. **Code syntax highlighting** - Ensure color contrast in code blocks
+6. **Animations** - Add prefers-reduced-motion support
+7. **Focus management** - Restore focus after dialog close
+8. **Landmark navigation** - Skip to main content link
+
+---
+
+## References
+
+- [WCAG 2.1 Guidelines](https://www.w3.org/WAI/WCAG21/quickref/)
+- [ARIA Authoring Practices](https://www.w3.org/WAI/ARIA/apg/)
+- [Material Design 3 Accessibility](https://m3.material.io/foundations/accessible-design)
+- [React Accessibility Guide](https://reactjs.org/docs/accessibility.html)
+
diff --git a/jest.setup.ts b/jest.setup.ts
index 3cb927e..b24a0d6 100644
--- a/jest.setup.ts
+++ b/jest.setup.ts
@@ -4,6 +4,19 @@ import React from 'react'
 // Make React globally available for components that may reference it
 global.React = React
 
+// Mock import.meta for Vite compatibility
+Object.defineProperty(globalThis, 'import', {
+  value: {
+    meta: {
+      env: {
+        DEV: false,
+        PROD: true,
+        SSR: false,
+      },
+    },
+  },
+})
+
 // Mock Next.js router
 jest.mock('next/router', () => ({
   useRouter: () => ({
diff --git a/src/components/demo/DemoFeatureCards.tsx b/src/components/demo/DemoFeatureCards.tsx
index d69a751..1bdbafa 100644
--- a/src/components/demo/DemoFeatureCards.tsx
+++ b/src/components/demo/DemoFeatureCards.tsx
@@ -4,8 +4,13 @@ import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
 
 export const DemoFeatureCards = () => {
   return (
-    <div className="grid grid-cols-1 md:grid-cols-3 gap-6">
-      <Card className="border-primary/20">
+    <div
+      className="grid grid-cols-1 md:grid-cols-3 gap-6"
+      data-testid="demo-feature-cards"
+      role="region"
+      aria-label="Feature cards"
+    >
+      <Card className="border-primary/20" data-testid="feature-card-realtime">
         <CardHeader>
           <CardTitle className="text-lg">Real-Time Updates</CardTitle>
         </CardHeader>
@@ -14,7 +19,7 @@ export const DemoFeatureCards = () => {
         </CardContent>
       </Card>
 
-      <Card className="border-accent/20">
+      <Card className="border-accent/20" data-testid="feature-card-resizable">
         <CardHeader>
           <CardTitle className="text-lg">Resizable Panels</CardTitle>
         </CardHeader>
@@ -23,7 +28,7 @@ export const DemoFeatureCards = () => {
         </CardContent>
       </Card>
 
-      <Card className="border-primary/20">
+      <Card className="border-primary/20" data-testid="feature-card-viewmodes">
         <CardHeader>
           <CardTitle className="text-lg">Multiple View Modes</CardTitle>
         </CardHeader>
diff --git a/src/components/features/snippet-editor/CodeEditorSection.tsx b/src/components/features/snippet-editor/CodeEditorSection.tsx
index a0e56c1..05a05c3 100644
--- a/src/components/features/snippet-editor/CodeEditorSection.tsx
+++ b/src/components/features/snippet-editor/CodeEditorSection.tsx
@@ -36,8 +36,14 @@ export function CodeEditorSection({
             id="hasPreview"
             checked={hasPreview}
             onCheckedChange={(checked) => onPreviewChange(checked as boolean)}
+            data-testid="enable-preview-checkbox"
+            aria-label="Enable live preview"
           />
-          <Label htmlFor="hasPreview" className="text-sm font-normal cursor-pointer">
+          <Label
+            htmlFor="hasPreview"
+            className="text-sm font-normal cursor-pointer"
+            data-testid="enable-preview-label"
+          >
             Enable live preview
           </Label>
         </div>
@@ -46,7 +52,10 @@ export function CodeEditorSection({
       <div className="space-y-2">
         <Label htmlFor="code">Code *</Label>
         {hasPreview && isPreviewSupported ? (
-          <div className={errors.code ? 'ring-2 ring-destructive/20 rounded-md' : ''}>
+          <div
+            className={errors.code ? 'ring-2 ring-destructive/20 rounded-md' : ''}
+            data-testid="split-screen-editor-container"
+          >
             <SplitScreenEditor
               value={code}
               onChange={onCodeChange}
@@ -61,11 +70,16 @@ export function CodeEditorSection({
             className={`rounded-md border overflow-hidden ${
               errors.code ? 'border-destructive ring-2 ring-destructive/20' : 'border-border'
             }`}
+            data-testid="code-editor-container"
           >
             <MonacoEditor value={code} onChange={onCodeChange} language={language} height="400px" />
           </div>
         )}
-        {errors.code && <p className="text-sm text-destructive">{errors.code}</p>}
+        {errors.code && (
+          <p className="text-sm text-destructive" id="code-error" data-testid="code-error-message">
+            {errors.code}
+          </p>
+        )}
       </div>
     </>
   )
diff --git a/src/components/features/snippet-editor/ReactPreview.tsx b/src/components/features/snippet-editor/ReactPreview.tsx
index 50b4155..7909429 100644
--- a/src/components/features/snippet-editor/ReactPreview.tsx
+++ b/src/components/features/snippet-editor/ReactPreview.tsx
@@ -33,9 +33,14 @@ export function ReactPreview({ code, language, functionName, inputParameters }:
 
   if (!['JSX', 'TSX', 'JavaScript', 'TypeScript'].includes(language)) {
     return (
-      <div className="h-full flex items-center justify-center p-6 bg-muted/30">
+      <div
+        className="h-full flex items-center justify-center p-6 bg-muted/30"
+        data-testid="preview-unsupported"
+        role="status"
+        aria-label="Preview not available"
+      >
         <div className="text-center text-muted-foreground">
-          <WarningCircle className="h-12 w-12 mx-auto mb-3 opacity-50" />
+          <WarningCircle className="h-12 w-12 mx-auto mb-3 opacity-50" aria-hidden="true" />
           <p className="text-sm">Preview not available for {language}</p>
           <p className="text-xs mt-1">Use JSX, TSX, JavaScript, or TypeScript</p>
         </div>
@@ -45,15 +50,19 @@ export function ReactPreview({ code, language, functionName, inputParameters }:
 
   if (error) {
     return (
-      <div className="h-full overflow-auto p-6 bg-destructive/5">
-        <Alert variant="destructive" className="mb-4">
-          <WarningCircle className="h-4 w-4" />
-          <AlertDescription className="font-mono text-xs whitespace-pre-wrap">
+      <div
+        className="h-full overflow-auto p-6 bg-destructive/5"
+        data-testid="preview-error"
+        role="alert"
+      >
+        <Alert variant="destructive" className="mb-4" data-testid="preview-error-alert">
+          <WarningCircle className="h-4 w-4" aria-hidden="true" />
+          <AlertDescription className="font-mono text-xs whitespace-pre-wrap" data-testid="preview-error-message">
             {error}
           </AlertDescription>
         </Alert>
-        <AIErrorHelper 
-          error={error} 
+        <AIErrorHelper
+          error={error}
           context={`React component preview rendering (Language: ${language})`}
         />
       </div>
@@ -62,7 +71,12 @@ export function ReactPreview({ code, language, functionName, inputParameters }:
 
   if (!Component) {
     return (
-      <div className="h-full flex items-center justify-center p-6 bg-muted/30">
+      <div
+        className="h-full flex items-center justify-center p-6 bg-muted/30"
+        data-testid="preview-loading"
+        role="status"
+        aria-label="Loading preview"
+      >
         <div className="text-center text-muted-foreground">
           <p className="text-sm">Loading preview...</p>
         </div>