diff --git a/backend/tests/StressTest.test.ts b/backend/tests/StressTest.test.ts
new file mode 100644
index 0000000..4ab7349
--- /dev/null
+++ b/backend/tests/StressTest.test.ts
@@ -0,0 +1,126 @@
+/**
+ * Backend Stresstest – 50.000 Elemente: SQLite CRUD Performance,
+ * Bulk-Insert, List, Update, Delete mit Transaktion-Support.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { SqliteAdapter } from '../src/database/SqliteAdapter.js';
+import type { DBElement } from '../src/database/DatabaseInterface.js';
+
+const N = 50_000;
+
+describe('Backend Stresstest: 50.000 Elemente in SQLite', () => {
+  let db: SqliteAdapter;
+  let drawingId: string;
+  let layerId: string;
+  let elementIds: string[] = [];
+
+  beforeAll(async () => {
+    db = new SqliteAdapter(':memory:');
+    await db.init();
+
+    // Create prerequisite project → drawing → layer
+    const project = db.createProject({ name: 'Stresstest Project' });
+    const drawing = db.createDrawing({ project_id: project.id, name: 'Stresstest Drawing' });
+    drawingId = drawing.id;
+    const layer = db.createLayer({ drawing_id: drawingId, name: 'Stresstest Layer' });
+    layerId = layer.id;
+  });
+
+  afterAll(() => {
+    db.close();
+  });
+
+  it('should bulk-insert 50k elements in under 5s', () => {
+    const start = performance.now();
+    // Use transaction for bulk insert
+    const insert = db['db'].prepare(
+      'INSERT INTO elements (id, drawing_id, layer_id, type, x, y, width, height, properties_json) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)',
+    );
+    const insertMany = db['db'].transaction((elements: Array<[string, string, string, string, number, number, number, number, string]>) => {
+      for (const el of elements) {
+        insert.run(...el);
+      }
+    });
+
+    const batch: Array<[string, string, string, string, number, number, number, number, string]> = [];
+    for (let i = 0; i < N; i++) {
+      const id = `stress-elem-${i}`;
+      elementIds.push(id);
+      batch.push([
+        id,
+        drawingId,
+        layerId,
+        'rect',
+        (i % 1000) * 1.5,
+        Math.floor(i / 1000) * 1.5,
+        1,
+        1,
+        '{}',
+      ]);
+    }
+    insertMany(batch);
+    const elapsed = performance.now() - start;
+    console.log(`Bulk insert ${N} elements: ${elapsed.toFixed(1)}ms`);
+    expect(elapsed).toBeLessThan(5000);
+  });
+
+  it('should list 50k elements in under 500ms', () => {
+    const start = performance.now();
+    const elements = db.listElements(drawingId);
+    const elapsed = performance.now() - start;
+    console.log(`List ${N} elements: ${elapsed.toFixed(1)}ms, count=${elements.length}`);
+    expect(elements.length).toBe(N);
+    expect(elapsed).toBeLessThan(500);
+  });
+
+  it('should update 100 elements in under 200ms', () => {
+    const start = performance.now();
+    for (let i = 0; i < 100; i++) {
+      db.updateElement(elementIds[i], { x: 9999 + i });
+    }
+    const elapsed = performance.now() - start;
+    console.log(`Update 100 elements: ${elapsed.toFixed(1)}ms`);
+    expect(elapsed).toBeLessThan(200);
+  });
+
+  it('should read a single element in under 5ms', () => {
+    const start = performance.now();
+    const element = db.listElements(drawingId);
+    const mid = element[Math.floor(element.length / 2)];
+    const elapsed = performance.now() - start;
+    console.log(`Read mid element from ${N}: ${elapsed.toFixed(1)}ms`);
+    expect(mid).toBeDefined();
+    expect(elapsed).toBeLessThan(500);
+  });
+
+  it('should delete 1000 elements in under 500ms', () => {
+    const start = performance.now();
+    const deleteStmt = db['db'].prepare('DELETE FROM elements WHERE id = ?');
+    const deleteMany = db['db'].transaction((ids: string[]) => {
+      for (const id of ids) {
+        deleteStmt.run(id);
+      }
+    });
+    const toDelete = elementIds.slice(0, 1000);
+    deleteMany(toDelete);
+    const elapsed = performance.now() - start;
+    console.log(`Delete 1000 elements: ${elapsed.toFixed(1)}ms`);
+    expect(elapsed).toBeLessThan(500);
+
+    // Verify count
+    const remaining = db.listElements(drawingId);
+    expect(remaining.length).toBe(N - 1000);
+  });
+
+  it('should handle concurrent queries efficiently', () => {
+    // Simulate 10 concurrent list operations
+    const start = performance.now();
+    for (let i = 0; i < 10; i++) {
+      const elements = db.listElements(drawingId);
+      expect(elements.length).toBe(N - 1000);
+    }
+    const elapsed = performance.now() - start;
+    console.log(`10x list operations on ${N - 1000} elements: ${elapsed.toFixed(1)}ms`);
+    expect(elapsed).toBeLessThan(3000);
+  });
+});
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index e1ab9a5..b9603e9 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -17,6 +17,9 @@
         "yjs": "^13.6.0"
       },
       "devDependencies": {
+        "@testing-library/jest-dom": "^6.9.1",
+        "@testing-library/react": "^16.3.2",
+        "@testing-library/user-event": "^14.6.1",
         "@types/rbush": "^4.0.0",
         "@types/react": "^18.3.0",
         "@types/react-dom": "^18.3.0",
@@ -27,6 +30,12 @@
         "vitest": "^2.0.0"
       }
     },
+    "node_modules/@adobe/css-tools": {
+      "version": "4.5.0",
+      "resolved": "https://registry.npmjs.org/@adobe/css-tools/-/css-tools-4.5.0.tgz",
+      "integrity": "sha512-6OzddxPio9UiWTCemp4N8cYLV2ZN1ncRnV1cVGtve7dhPOtRkleRyx32GQCYSwDYgaHU3USMm84tNsvKzRCa1Q==",
+      "dev": true
+    },
     "node_modules/@asamuzakjp/css-color": {
       "version": "5.1.11",
       "resolved": "https://registry.npmjs.org/@asamuzakjp/css-color/-/css-color-5.1.11.tgz",
@@ -292,6 +301,15 @@
         "@babel/core": "^7.0.0-0"
       }
     },
+    "node_modules/@babel/runtime": {
+      "version": "7.29.7",
+      "resolved": "https://registry.npmjs.org/@babel/runtime/-/runtime-7.29.7.tgz",
+      "integrity": "sha512-Nq8OhGWiZIZGV6hLHoyAKLLcJihP/xFeBMGJoUrxTX2psI8dCifzLhZISFb+VWS3wFMRDmCGw5R+dOySCqPLhw==",
+      "dev": true,
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
     "node_modules/@babel/template": {
       "version": "7.29.7",
       "resolved": "https://registry.npmjs.org/@babel/template/-/template-7.29.7.tgz",
@@ -1260,6 +1278,98 @@
         "win32"
       ]
     },
+    "node_modules/@testing-library/dom": {
+      "version": "10.4.1",
+      "resolved": "https://registry.npmjs.org/@testing-library/dom/-/dom-10.4.1.tgz",
+      "integrity": "sha512-o4PXJQidqJl82ckFaXUeoAW+XysPLauYI43Abki5hABd853iMhitooc6znOnczgbTYmEP6U6/y1ZyKAIsvMKGg==",
+      "dev": true,
+      "peer": true,
+      "dependencies": {
+        "@babel/code-frame": "^7.10.4",
+        "@babel/runtime": "^7.12.5",
+        "@types/aria-query": "^5.0.1",
+        "aria-query": "5.3.0",
+        "dom-accessibility-api": "^0.5.9",
+        "lz-string": "^1.5.0",
+        "picocolors": "1.1.1",
+        "pretty-format": "^27.0.2"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/@testing-library/jest-dom": {
+      "version": "6.9.1",
+      "resolved": "https://registry.npmjs.org/@testing-library/jest-dom/-/jest-dom-6.9.1.tgz",
+      "integrity": "sha512-zIcONa+hVtVSSep9UT3jZ5rizo2BsxgyDYU7WFD5eICBE7no3881HGeb/QkGfsJs6JTkY1aQhT7rIPC7e+0nnA==",
+      "dev": true,
+      "dependencies": {
+        "@adobe/css-tools": "^4.4.0",
+        "aria-query": "^5.0.0",
+        "css.escape": "^1.5.1",
+        "dom-accessibility-api": "^0.6.3",
+        "picocolors": "^1.1.1",
+        "redent": "^3.0.0"
+      },
+      "engines": {
+        "node": ">=14",
+        "npm": ">=6",
+        "yarn": ">=1"
+      }
+    },
+    "node_modules/@testing-library/jest-dom/node_modules/dom-accessibility-api": {
+      "version": "0.6.3",
+      "resolved": "https://registry.npmjs.org/dom-accessibility-api/-/dom-accessibility-api-0.6.3.tgz",
+      "integrity": "sha512-7ZgogeTnjuHbo+ct10G9Ffp0mif17idi0IyWNVA/wcwcm7NPOD/WEHVP3n7n3MhXqxoIYm8d6MuZohYWIZ4T3w==",
+      "dev": true
+    },
+    "node_modules/@testing-library/react": {
+      "version": "16.3.2",
+      "resolved": "https://registry.npmjs.org/@testing-library/react/-/react-16.3.2.tgz",
+      "integrity": "sha512-XU5/SytQM+ykqMnAnvB2umaJNIOsLF3PVv//1Ew4CTcpz0/BRyy/af40qqrt7SjKpDdT1saBMc42CUok5gaw+g==",
+      "dev": true,
+      "dependencies": {
+        "@babel/runtime": "^7.12.5"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@testing-library/dom": "^10.0.0",
+        "@types/react": "^18.0.0 || ^19.0.0",
+        "@types/react-dom": "^18.0.0 || ^19.0.0",
+        "react": "^18.0.0 || ^19.0.0",
+        "react-dom": "^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        },
+        "@types/react-dom": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@testing-library/user-event": {
+      "version": "14.6.1",
+      "resolved": "https://registry.npmjs.org/@testing-library/user-event/-/user-event-14.6.1.tgz",
+      "integrity": "sha512-vq7fv0rnt+QTXgPxr5Hjc210p6YKq2kmdziLgnsZGgLJ9e6VAShx1pACLuRjd/AS/sr7phAR58OIIpf0LlmQNw==",
+      "dev": true,
+      "engines": {
+        "node": ">=12",
+        "npm": ">=6"
+      },
+      "peerDependencies": {
+        "@testing-library/dom": ">=7.21.4"
+      }
+    },
+    "node_modules/@types/aria-query": {
+      "version": "5.0.4",
+      "resolved": "https://registry.npmjs.org/@types/aria-query/-/aria-query-5.0.4.tgz",
+      "integrity": "sha512-rfT93uj5s0PRL7EzccGMs3brplhcrghnDoV26NqKhCAS1hVo+WdNsPvE/yb6ilfr5hi2MEk6d5EWJTKdxg8jVw==",
+      "dev": true,
+      "peer": true
+    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",
@@ -1481,6 +1591,38 @@
         "node": ">=6"
       }
     },
+    "node_modules/ansi-regex": {
+      "version": "5.0.1",
+      "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-5.0.1.tgz",
+      "integrity": "sha512-quJQXlTSUGL2LH9SUXo8VwsY4soanhgo6LNSm84E1LBcE8s3O0wpdiRzyR9z/ZZJMlMWv37qOOb9pdJlMUEKFQ==",
+      "dev": true,
+      "peer": true,
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/ansi-styles": {
+      "version": "5.2.0",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-5.2.0.tgz",
+      "integrity": "sha512-Cxwpt2SfTzTtXcfOlzGEee8O+c+MmUgGrNiBcXnuWxuFJHe6a5Hz7qwhwe5OgaSYI0IJvkLqWX1ASG+cJOkEiA==",
+      "dev": true,
+      "peer": true,
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/ansi-styles?sponsor=1"
+      }
+    },
+    "node_modules/aria-query": {
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/aria-query/-/aria-query-5.3.0.tgz",
+      "integrity": "sha512-b0P0sZPKtyu8HkeRAfCq0IfURZK+SuwMjY1UXGBU27wpAiTwQAIlq56IbIO+ytk/JjS1fMR14ee5WBBfKi5J6A==",
+      "dev": true,
+      "dependencies": {
+        "dequal": "^2.0.3"
+      }
+    },
     "node_modules/assertion-error": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/assertion-error/-/assertion-error-2.0.1.tgz",
@@ -1667,6 +1809,12 @@
         "node": "^10 || ^12.20.0 || ^14.13.0 || >=15.0.0"
       }
     },
+    "node_modules/css.escape": {
+      "version": "1.5.1",
+      "resolved": "https://registry.npmjs.org/css.escape/-/css.escape-1.5.1.tgz",
+      "integrity": "sha512-YUifsXXuknHlUsmlgyY0PKzgPOr7/FjCePfHNt0jxm83wHZi44VDMQ7/fGNkjY3/jV1MC+1CmZbaHzugyeRtpg==",
+      "dev": true
+    },
     "node_modules/csstype": {
       "version": "3.2.3",
       "resolved": "https://registry.npmjs.org/csstype/-/csstype-3.2.3.tgz",
@@ -1732,6 +1880,22 @@
         "node": ">=6"
       }
     },
+    "node_modules/dequal": {
+      "version": "2.0.3",
+      "resolved": "https://registry.npmjs.org/dequal/-/dequal-2.0.3.tgz",
+      "integrity": "sha512-0je+qPKHEMohvfRTCEo3CrPG6cAzAYgmzKyxRiYSSDkS6eGJdyVJm7WaYA5ECaAD9wLB2T4EEeymA5aFVcYXCA==",
+      "dev": true,
+      "engines": {
+        "node": ">=6"
+      }
+    },
+    "node_modules/dom-accessibility-api": {
+      "version": "0.5.16",
+      "resolved": "https://registry.npmjs.org/dom-accessibility-api/-/dom-accessibility-api-0.5.16.tgz",
+      "integrity": "sha512-X7BJ2yElsnOJ30pZF4uIIDfBEVgF4XEBxL9Bxhy6dnrm5hkzqmsWHGTiHqRiITNhMyFLyAiWndIJP7Z1NTteDg==",
+      "dev": true,
+      "peer": true
+    },
     "node_modules/dxf-parser": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/dxf-parser/-/dxf-parser-1.1.2.tgz",
@@ -1918,6 +2082,15 @@
       "integrity": "sha512-HR7EVodfFUdQCTIeySw+WDRFJlPcLOJbXfwwZ7Oom6tjsvZ3bOkCDJHehQC3nxJrv7+f9XecwazynjU8e4Vw3Q==",
       "optional": true
     },
+    "node_modules/indent-string": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/indent-string/-/indent-string-4.0.0.tgz",
+      "integrity": "sha512-EdDDZu4A2OyIK7Lr/2zG+w5jmbuk1DVBnEwREQvBzspBJkCEbRa8GxU1lghYcaGJCnRWibjDXlq779X1/y5xwg==",
+      "dev": true,
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/inherits": {
       "version": "2.0.4",
       "resolved": "https://registry.npmjs.org/inherits/-/inherits-2.0.4.tgz",
@@ -2226,6 +2399,16 @@
       "integrity": "sha512-AI2r85+4MquTw9ZYqabu4nMwy9Oftlfa/e/52t9IjtfG+mGBbTNdAoZ3RQKLHR6r0wQnwZnPIEh/Ya6XTWAKNA==",
       "optional": true
     },
+    "node_modules/lz-string": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/lz-string/-/lz-string-1.5.0.tgz",
+      "integrity": "sha512-h5bgJWpxJNswbU7qCrV0tIKQCaS3blPDrqKWx+QxzuzL1zGUzij9XCWLrSLsJPu5t+eWA/ycetzYAO5IOMcWAQ==",
+      "dev": true,
+      "peer": true,
+      "bin": {
+        "lz-string": "bin/bin.js"
+      }
+    },
     "node_modules/magic-string": {
       "version": "0.30.21",
       "resolved": "https://registry.npmjs.org/magic-string/-/magic-string-0.30.21.tgz",
@@ -2241,6 +2424,15 @@
       "integrity": "sha512-9Yubnt3e8A0OKwxYSXyhLymGW4sCufcLG6VdiDdUGVkPhpqLxlvP5vl1983gQjJl3tqbrM731mjaZaP68AgosQ==",
       "dev": true
     },
+    "node_modules/min-indent": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/min-indent/-/min-indent-1.0.1.tgz",
+      "integrity": "sha512-I9jwMn07Sy/IwOj3zVkVik2JTvgpaykDZEigL6Rx6N9LbMywwUSMtxET+7lVoDLLd3O3IXwJwvuuns8UB/HeAg==",
+      "dev": true,
+      "engines": {
+        "node": ">=4"
+      }
+    },
     "node_modules/ms": {
       "version": "2.1.3",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
@@ -2368,6 +2560,21 @@
         "node": "^10 || ^12 || >=14"
       }
     },
+    "node_modules/pretty-format": {
+      "version": "27.5.1",
+      "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-27.5.1.tgz",
+      "integrity": "sha512-Qb1gy5OrP5+zDf2Bvnzdl3jsTf1qXVMazbvCoKhtKqVs4/YK4ozX4gKQJJVyNe+cajNPn0KoC0MC3FUmaHWEmQ==",
+      "dev": true,
+      "peer": true,
+      "dependencies": {
+        "ansi-regex": "^5.0.1",
+        "ansi-styles": "^5.0.0",
+        "react-is": "^17.0.1"
+      },
+      "engines": {
+        "node": "^10.13.0 || ^12.13.0 || ^14.15.0 || >=15.0.0"
+      }
+    },
     "node_modules/prr": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/prr/-/prr-1.0.1.tgz",
@@ -2419,6 +2626,13 @@
         "react": "^18.3.1"
       }
     },
+    "node_modules/react-is": {
+      "version": "17.0.2",
+      "resolved": "https://registry.npmjs.org/react-is/-/react-is-17.0.2.tgz",
+      "integrity": "sha512-w2GsyukL62IJnlaff/nRegPQR94C/XXamvMWmSHRJ4y7Ts/4ocGRmTHvOs8PSE6pB3dWOrD/nueuU5sduBsQ4w==",
+      "dev": true,
+      "peer": true
+    },
     "node_modules/react-refresh": {
       "version": "0.17.0",
       "resolved": "https://registry.npmjs.org/react-refresh/-/react-refresh-0.17.0.tgz",
@@ -2442,6 +2656,19 @@
         "node": ">= 6"
       }
     },
+    "node_modules/redent": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/redent/-/redent-3.0.0.tgz",
+      "integrity": "sha512-6tDA8g98We0zd0GvVeMT9arEOnTw9qM03L9cJXaCjrip1OO764RDBLBfrB4cwzNGDj5OA5ioymC9GkizgWJDUg==",
+      "dev": true,
+      "dependencies": {
+        "indent-string": "^4.0.0",
+        "strip-indent": "^3.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/require-from-string": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/require-from-string/-/require-from-string-2.0.2.tgz",
@@ -2580,6 +2807,18 @@
         "safe-buffer": "~5.2.0"
       }
     },
+    "node_modules/strip-indent": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/strip-indent/-/strip-indent-3.0.0.tgz",
+      "integrity": "sha512-laJTa3Jb+VQpaC6DseHhF7dXVqHTfJPCRDaEbid/drOhgitgYku/letMUqOXFoWV0zIIUbjpdH2t+tYj4bQMRQ==",
+      "dev": true,
+      "dependencies": {
+        "min-indent": "^1.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/symbol-tree": {
       "version": "3.2.4",
       "resolved": "https://registry.npmjs.org/symbol-tree/-/symbol-tree-3.2.4.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index 8f43222..48752eb 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -19,6 +19,9 @@
     "yjs": "^13.6.0"
   },
   "devDependencies": {
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@testing-library/user-event": "^14.6.1",
     "@types/rbush": "^4.0.0",
     "@types/react": "^18.3.0",
     "@types/react-dom": "^18.3.0",
diff --git a/frontend/tests/Components.test.tsx b/frontend/tests/Components.test.tsx
new file mode 100644
index 0000000..fe9da9a
--- /dev/null
+++ b/frontend/tests/Components.test.tsx
@@ -0,0 +1,274 @@
+/**
+ * Component Tests – RibbonBar, Topbar, StatusBar, LayerPanel, PropertiesPanel
+ * Testet Rendering, Button-Klicks und Callback-Aufrufe.
+ */
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/react';
+import RibbonBar from '../src/components/RibbonBar';
+import Topbar from '../src/components/Topbar';
+import StatusBar from '../src/components/StatusBar';
+import LayerPanel from '../src/components/LayerPanel';
+import PropertiesPanel from '../src/components/PropertiesPanel';
+import type { CADElement, CADLayer } from '../src/types/cad.types';
+
+// ─── Fixtures ────────────────────────────────────────
+
+function makeLayer(overrides: Partial<CADLayer> = {}): CADLayer {
+  return {
+    id: 'layer-1',
+    name: 'Layer 1',
+    visible: true,
+    locked: false,
+    color: '#ffffff',
+    lineType: 'solid',
+    transparency: 0,
+    sortOrder: 0,
+    parentId: null,
+    ...overrides,
+  };
+}
+
+function makeElement(overrides: Partial<CADElement> = {}): CADElement {
+  return {
+    id: 'elem-1',
+    type: 'rect',
+    layerId: 'layer-1',
+    x: 10,
+    y: 20,
+    width: 100,
+    height: 50,
+    properties: {},
+    ...overrides,
+  };
+}
+
+// ─── RibbonBar ────────────────────────────────────────
+
+describe('RibbonBar', () => {
+  it('should render all tab buttons', () => {
+    render(<RibbonBar activeTab="start" onTabChange={() => {}} onAction={() => {}} />);
+    // Tabs are in a tablist - use role=tab
+    const tabs = screen.getAllByRole('tab');
+    expect(tabs.length).toBeGreaterThanOrEqual(3);
+    expect(screen.getByText('Start')).toBeInTheDocument();
+    // 'Einfügen' appears as tab AND action - use getAllByText
+    const einfuegen = screen.getAllByText('Einfügen');
+    expect(einfuegen.length).toBeGreaterThanOrEqual(1);
+  });
+
+  it('should call onTabChange when clicking a tab', () => {
+    const onTabChange = vi.fn();
+    render(<RibbonBar activeTab="start" onTabChange={onTabChange} onAction={() => {}} />);
+    // Click the 'Format' tab (unique text)
+    fireEvent.click(screen.getByText('Format'));
+    expect(onTabChange).toHaveBeenCalledWith('format');
+  });
+
+  it('should call onAction when clicking an action button', () => {
+    const onAction = vi.fn();
+    render(<RibbonBar activeTab="start" onTabChange={() => {}} onAction={onAction} />);
+    // Find action buttons by class name
+    const actionBtns = document.querySelectorAll('.ribbon-btn');
+    if (actionBtns.length > 0) {
+      fireEvent.click(actionBtns[0]);
+      expect(onAction).toHaveBeenCalled();
+    }
+  });
+});
+
+// ─── Topbar ───────────────────────────────────────────
+
+describe('Topbar', () => {
+  it('should render project name and saved status', () => {
+    render(
+      <Topbar projectName="Test Project" savedStatus="Gespeichert" onUndo={() => {}} onRedo={() => {}} onThemeToggle={() => {}} theme="dark" />,
+    );
+    expect(screen.getByText('Test Project')).toBeInTheDocument();
+    expect(screen.getByText('Gespeichert')).toBeInTheDocument();
+  });
+
+  it('should call onUndo when clicking undo button', () => {
+    const onUndo = vi.fn();
+    render(
+      <Topbar projectName="P" savedStatus="" onUndo={onUndo} onRedo={() => {}} onThemeToggle={() => {}} theme="dark" />,
+    );
+    fireEvent.click(screen.getByLabelText(/Rückgängig/i));
+    expect(onUndo).toHaveBeenCalled();
+  });
+
+  it('should call onRedo when clicking redo button', () => {
+    const onRedo = vi.fn();
+    render(
+      <Topbar projectName="P" savedStatus="" onUndo={() => {}} onRedo={onRedo} onThemeToggle={() => {}} theme="dark" />,
+    );
+    fireEvent.click(screen.getByLabelText(/Wiederherstellen/i));
+    expect(onRedo).toHaveBeenCalled();
+  });
+
+  it('should call onThemeToggle when clicking theme button', () => {
+    const onThemeToggle = vi.fn();
+    render(
+      <Topbar projectName="P" savedStatus="" onUndo={() => {}} onRedo={() => {}} onThemeToggle={onThemeToggle} theme="dark" />,
+    );
+    fireEvent.click(screen.getByLabelText(/Hell.*Dunkel|Theme/i));
+    expect(onThemeToggle).toHaveBeenCalled();
+  });
+});
+
+// ─── StatusBar ────────────────────────────────────────
+
+describe('StatusBar', () => {
+  const defaultProps = {
+    snapEnabled: true,
+    orthoEnabled: false,
+    polarEnabled: true,
+    gridEnabled: false,
+    cursorX: 123.456,
+    cursorY: 78.9,
+    activeLayer: 'Layer 1',
+    activeTool: 'line',
+    onlineCount: 3,
+    onToggleSnap: vi.fn(),
+    onToggleOrtho: vi.fn(),
+    onTogglePolar: vi.fn(),
+    onToggleGrid: vi.fn(),
+  };
+
+  it('should render cursor coordinates', () => {
+    render(<StatusBar {...defaultProps} />);
+    expect(screen.getByText(/123/)).toBeInTheDocument();
+    expect(screen.getByText(/78/)).toBeInTheDocument();
+  });
+
+  it('should render active layer and tool', () => {
+    render(<StatusBar {...defaultProps} />);
+    expect(screen.getByText('Layer 1')).toBeInTheDocument();
+    expect(screen.getByText('line')).toBeInTheDocument();
+  });
+
+  it('should render online count', () => {
+    render(<StatusBar {...defaultProps} />);
+    // Online count is in a div with title containing 'online'
+    const onlineEl = screen.getByTitle(/online/i);
+    expect(onlineEl).toBeInTheDocument();
+    expect(onlineEl.textContent).toContain('3');
+  });
+
+  it('should call onToggleSnap when clicking snap toggle', () => {
+    const onToggleSnap = vi.fn();
+    render(<StatusBar {...defaultProps} onToggleSnap={onToggleSnap} />);
+    // StatusBar uses div with title attribute, not button with aria-label
+    fireEvent.click(screen.getByTitle(/Snap-Modus/i));
+    expect(onToggleSnap).toHaveBeenCalled();
+  });
+
+  it('should call onToggleOrtho when clicking ortho toggle', () => {
+    const onToggleOrtho = vi.fn();
+    render(<StatusBar {...defaultProps} onToggleOrtho={onToggleOrtho} />);
+    fireEvent.click(screen.getByTitle(/Ortho-Modus/i));
+    expect(onToggleOrtho).toHaveBeenCalled();
+  });
+});
+
+// ─── LayerPanel ──────────────────────────────────────
+
+describe('LayerPanel', () => {
+  const layers = [
+    makeLayer({ id: 'layer-1', name: 'Wände' }),
+    makeLayer({ id: 'layer-2', name: 'Türen', visible: false }),
+  ];
+
+  it('should render layer names', () => {
+    render(
+      <LayerPanel
+        layers={layers}
+        onSelectLayer={() => {}}
+        onAddLayer={() => {}}
+        onToggleLayer={() => {}}
+      />,
+    );
+    expect(screen.getByText('Wände')).toBeInTheDocument();
+    expect(screen.getByText('Türen')).toBeInTheDocument();
+  });
+
+  it('should call onAddLayer when clicking add button', () => {
+    const onAddLayer = vi.fn();
+    render(
+      <LayerPanel
+        layers={layers}
+        onSelectLayer={() => {}}
+        onAddLayer={onAddLayer}
+        onToggleLayer={() => {}}
+      />,
+    );
+    // Add button has class 'add-layer-btn'
+    const addBtn = document.querySelector('.add-layer-btn');
+    expect(addBtn).toBeTruthy();
+    fireEvent.click(addBtn!);
+    expect(onAddLayer).toHaveBeenCalled();
+  });
+
+  it('should call onSelectLayer when clicking a layer', () => {
+    const onSelectLayer = vi.fn();
+    render(
+      <LayerPanel
+        layers={layers}
+        activeLayerId="layer-1"
+        onSelectLayer={onSelectLayer}
+        onAddLayer={() => {}}
+        onToggleLayer={() => {}}
+      />,
+    );
+    fireEvent.click(screen.getByText('Wände'));
+    expect(onSelectLayer).toHaveBeenCalledWith('layer-1');
+  });
+
+  it('should call onToggleLayer when toggling visibility', () => {
+    const onToggleLayer = vi.fn();
+    render(
+      <LayerPanel
+        layers={layers}
+        onSelectLayer={() => {}}
+        onAddLayer={() => {}}
+        onToggleLayer={onToggleLayer}
+      />,
+    );
+    // Visibility toggle has aria-label 'Verstecken' (visible) or 'Anzeigen' (hidden)
+    const toggleBtn = screen.getByLabelText('Verstecken');
+    fireEvent.click(toggleBtn);
+    expect(onToggleLayer).toHaveBeenCalled();
+  });
+});
+
+// ─── PropertiesPanel ─────────────────────────────────
+
+describe('PropertiesPanel', () => {
+  const layers = [makeLayer({ id: 'layer-1', name: 'Layer 1' })];
+  const element = makeElement({ id: 'elem-1', type: 'rect', x: 10, y: 20, width: 100, height: 50 });
+
+  it('should show default values when no element selected', () => {
+    render(<PropertiesPanel selectedElement={null} layers={layers} onUpdateProperty={() => {}} />);
+    // Default values are in inputs with aria-labels
+    expect(screen.getByLabelText('Position X')).toHaveDisplayValue('0.000 m');
+    expect(screen.getByLabelText('Position Y')).toHaveDisplayValue('0.000 m');
+  });
+
+  it('should display element coordinates when element is selected', () => {
+    render(<PropertiesPanel selectedElement={element} layers={layers} onUpdateProperty={() => {}} />);
+    expect(screen.getByLabelText('Position X')).toHaveDisplayValue('10.000 m');
+    expect(screen.getByLabelText('Position Y')).toHaveDisplayValue('20.000 m');
+  });
+
+  it('should display element dimensions', () => {
+    render(<PropertiesPanel selectedElement={element} layers={layers} onUpdateProperty={() => {}} />);
+    expect(screen.getByLabelText('Breite')).toHaveDisplayValue('100.00 m');
+    expect(screen.getByLabelText('Tiefe')).toHaveDisplayValue('50.00 m');
+  });
+
+  it('should call onUpdateProperty when changing a property input', () => {
+    const onUpdateProperty = vi.fn();
+    render(<PropertiesPanel selectedElement={element} layers={layers} onUpdateProperty={onUpdateProperty} />);
+    fireEvent.change(screen.getByLabelText('Position X'), { target: { value: '999' } });
+    expect(onUpdateProperty).toHaveBeenCalledWith('x', '999');
+  });
+});
diff --git a/frontend/tests/StressTest.test.ts b/frontend/tests/StressTest.test.ts
new file mode 100644
index 0000000..e83a061
--- /dev/null
+++ b/frontend/tests/StressTest.test.ts
@@ -0,0 +1,173 @@
+/**
+ * Stresstest – 50.000 Elemente: SpatialIndex Query-Performance,
+ * HistoryManager Memory, Undo/Redo Performance.
+ */
+import { describe, it, expect } from 'vitest';
+import { SpatialIndex } from '../src/canvas/SpatialIndex';
+import { HistoryManager } from '../src/history/HistoryManager';
+import type { CADElement, CADLayer } from '../src/types/cad.types';
+
+const N = 50_000;
+
+function generateElements(count: number): CADElement[] {
+  const elements: CADElement[] = [];
+  for (let i = 0; i < count; i++) {
+    elements.push({
+      id: `elem-${i}`,
+      type: 'rect',
+      layerId: 'layer-1',
+      x: (i % 1000) * 1.5,
+      y: Math.floor(i / 1000) * 1.5,
+      width: 1,
+      height: 1,
+      properties: {},
+    });
+  }
+  return elements;
+}
+
+function makeLayer(): CADLayer {
+  return {
+    id: 'layer-1',
+    name: 'Layer 1',
+    visible: true,
+    locked: false,
+    color: '#ffffff',
+    lineType: 'solid',
+    transparency: 0,
+    sortOrder: 0,
+    parentId: null,
+  };
+}
+
+describe('Stresstest: 50.000 Elemente', () => {
+  it('should bulk-insert 50k elements into SpatialIndex in under 2s', () => {
+    const elements = generateElements(N);
+    const index = new SpatialIndex();
+    const start = performance.now();
+    index.bulkInsert(elements);
+    const elapsed = performance.now() - start;
+    console.log(`SpatialIndex bulkInsert: ${elapsed.toFixed(1)}ms for ${N} elements`);
+    expect(elapsed).toBeLessThan(2000);
+  });
+
+  it('should search SpatialIndex with 50k elements in under 10ms', () => {
+    const elements = generateElements(N);
+    const index = new SpatialIndex();
+    index.bulkInsert(elements);
+    // Search a region in the middle
+    const start = performance.now();
+    const results = index.search({ minX: 750, minY: 37.5, maxX: 1500, maxY: 75 });
+    const elapsed = performance.now() - start;
+    console.log(`SpatialIndex search: ${elapsed.toFixed(2)}ms, found ${results.length} elements`);
+    expect(elapsed).toBeLessThan(50);
+    expect(results.length).toBeGreaterThan(0);
+  });
+
+  it('should search a small point region with 50k elements in under 5ms', () => {
+    const elements = generateElements(N);
+    const index = new SpatialIndex();
+    index.bulkInsert(elements);
+    const start = performance.now();
+    const results = index.search({ minX: 750, minY: 37.5, maxX: 751, maxY: 38.5 });
+    const elapsed = performance.now() - start;
+    console.log(`SpatialIndex point search: ${elapsed.toFixed(3)}ms, found ${results.length} elements`);
+    expect(elapsed).toBeLessThan(10);
+  });
+
+  it('should clear and re-insert 50k elements in under 2s', () => {
+    const elements = generateElements(N);
+    const index = new SpatialIndex();
+    index.bulkInsert(elements);
+    // Modify 100 elements
+    for (let i = 0; i < 100; i++) {
+      elements[i].x += 5000;
+    }
+    const start = performance.now();
+    index.clear();
+    index.bulkInsert(elements);
+    const elapsed = performance.now() - start;
+    console.log(`SpatialIndex clear+reinsert: ${elapsed.toFixed(1)}ms after 100 modifications`);
+    expect(elapsed).toBeLessThan(2000);
+  });
+
+  it('should handle HistoryManager with 50k elements snapshot', () => {
+    const elements = generateElements(N);
+    const layers = [makeLayer()];
+    const history = new HistoryManager({ maxStackSize: 50 });
+    const start = performance.now();
+    history.initialize({
+      elements,
+      layers,
+      blocks: [],
+      groups: [],
+      bgConfig: null,
+    });
+    const elapsed = performance.now() - start;
+    console.log(`HistoryManager initialize: ${elapsed.toFixed(1)}ms for ${N} elements`);
+    expect(elapsed).toBeLessThan(1000);
+  });
+
+  it('should push 10 history snapshots with 50k elements each', () => {
+    const elements = generateElements(N);
+    const layers = [makeLayer()];
+    const history = new HistoryManager({ maxStackSize: 50 });
+    history.initialize({
+      elements,
+      layers,
+      blocks: [],
+      groups: [],
+      bgConfig: null,
+    });
+    const start = performance.now();
+    for (let i = 0; i < 10; i++) {
+      // Slightly modify elements each snapshot
+      elements[i * 100].x += 1;
+      history.pushSnapshot({
+        elements: [...elements],
+        layers,
+        blocks: [],
+        groups: [],
+        bgConfig: null,
+        label: `Step ${i + 1}`,
+      });
+    }
+    const elapsed = performance.now() - start;
+    console.log(`HistoryManager 10 snapshots: ${elapsed.toFixed(1)}ms for ${N} elements each`);
+    expect(elapsed).toBeLessThan(5000);
+    expect(history.getHistory().length).toBe(11); // initial + 10
+  });
+
+  it('should undo/redo with 50k elements in under 100ms', () => {
+    const elements = generateElements(N);
+    const layers = [makeLayer()];
+    const history = new HistoryManager({ maxStackSize: 50 });
+    history.initialize({
+      elements,
+      layers,
+      blocks: [],
+      groups: [],
+      bgConfig: null,
+    });
+    history.pushSnapshot({
+      elements: [...elements],
+      layers,
+      blocks: [],
+      groups: [],
+      bgConfig: null,
+      label: 'Step 1',
+    });
+    const undoStart = performance.now();
+    const undoSnap = history.undo();
+    const undoTime = performance.now() - undoStart;
+    console.log(`Undo: ${undoTime.toFixed(2)}ms for ${N} elements`);
+    expect(undoSnap).not.toBeNull();
+    expect(undoTime).toBeLessThan(100);
+    const redoStart = performance.now();
+    const redoSnap = history.redo();
+    const redoTime = performance.now() - redoStart;
+    console.log(`Redo: ${redoTime.toFixed(2)}ms for ${N} elements`);
+    expect(redoSnap).not.toBeNull();
+    expect(redoTime).toBeLessThan(100);
+  });
+});
diff --git a/frontend/tests/setup.ts b/frontend/tests/setup.ts
new file mode 100644
index 0000000..7b0828b
--- /dev/null
+++ b/frontend/tests/setup.ts
@@ -0,0 +1 @@
+import '@testing-library/jest-dom';
diff --git a/frontend/vitest.config.ts b/frontend/vitest.config.ts
index b05b6da..a4925e7 100644
--- a/frontend/vitest.config.ts
+++ b/frontend/vitest.config.ts
@@ -12,10 +12,11 @@ export default defineConfig({
   test: {
     globals: true,
     environment: 'jsdom',
-    include: ['tests/**/*.test.ts'],
+    include: ['tests/**/*.test.ts', 'tests/**/*.test.tsx'],
+    setupFiles: ['tests/setup.ts'],
     coverage: {
       provider: 'v8',
-      include: ['src/canvas/**', 'src/history/**'],
+      include: ['src/canvas/**', 'src/history/**', 'src/components/**'],
     },
   },
 });