diff --git a/backend/src/routes/__tests__/blocks.test.ts b/backend/src/routes/__tests__/blocks.test.ts
new file mode 100644
index 0000000..cdf1fc1
--- /dev/null
+++ b/backend/src/routes/__tests__/blocks.test.ts
@@ -0,0 +1,172 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { fastify } from 'fastify';
+import blocksRoutes from '../blocks';
+import { BlockService } from '../../services/blockService';
+
+// Mock BlockService
+vi.mock('../../services/blockService', () => ({
+  BlockService: {
+    listBlocks: vi.fn(),
+    createBlock: vi.fn(),
+    updateBlock: vi.fn(),
+    deleteBlock: vi.fn(),
+    insertBlockInstance: vi.fn()
+  }
+}));
+
+// Mock auth middleware
+vi.mock('../middleware/auth', () => ({
+  authenticate: vi.fn(async (request, reply, done) => done()),
+  authorizeProjectMember: vi.fn(async (request, reply, done) => done()),
+  authorizePlanner: vi.fn(async (request, reply, done) => done())
+}));
+
+const app = fastify();
+app.register(blocksRoutes, { prefix: '/projects/:projectId/blocks' });
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe('GET /projects/:projectId/blocks', () => {
+  it('should return list of blocks', async () => {
+    const mockBlocks = [{ id: '1', name: 'Block 1' }];
+    (BlockService.listBlocks as vi.Mock).mockResolvedValue(mockBlocks);
+
+    const response = await app.inject({
+      method: 'GET',
+      url: '/projects/123/blocks'
+    });
+
+    expect(response.statusCode).toBe(200);
+    expect(JSON.parse(response.body)).toEqual(mockBlocks);
+  });
+
+  it('should handle errors', async () => {
+    (BlockService.listBlocks as vi.Mock).mockRejectedValue(new Error('Database error'));
+
+    const response = await app.inject({
+      method: 'GET',
+      url: '/projects/123/blocks'
+    });
+
+    expect(response.statusCode).toBe(500);
+    expect(JSON.parse(response.body)).toEqual({ error: 'Failed to list blocks' });
+  });
+});
+
+describe('POST /projects/:projectId/blocks', () => {
+  it('should create a new block', async () => {
+    const mockBlock = { id: '1', name: 'New Block' };
+    (BlockService.createBlock as vi.Mock).mockResolvedValue(mockBlock);
+
+    const response = await app.inject({
+      method: 'POST',
+      url: '/projects/123/blocks',
+      payload: {
+        name: 'New Block',
+        elements: ['element1', 'element2']
+      }
+    });
+
+    expect(response.statusCode).toBe(201);
+    expect(JSON.parse(response.body)).toEqual(mockBlock);
+  });
+
+  it('should handle validation errors', async () => {
+    const response = await app.inject({
+      method: 'POST',
+      url: '/projects/123/blocks',
+      payload: {
+        // name is missing
+        elements: ['element1', 'element2']
+      }
+    });
+
+    expect(response.statusCode).toBe(400);
+  });
+});
+
+describe('PUT /projects/:projectId/blocks/:blockId', () => {
+  it('should update a block', async () => {
+    const mockBlock = { id: '1', name: 'Updated Block' };
+    (BlockService.updateBlock as vi.Mock).mockResolvedValue(mockBlock);
+
+    const response = await app.inject({
+      method: 'PUT',
+      url: '/projects/123/blocks/1',
+      payload: {
+        name: 'Updated Block'
+      }
+    });
+
+    expect(response.statusCode).toBe(200);
+    expect(JSON.parse(response.body)).toEqual(mockBlock);
+  });
+
+  it('should handle validation errors', async () => {
+    const response = await app.inject({
+      method: 'PUT',
+      url: '/projects/123/blocks/invalid-id',
+      payload: {
+        name: 'Updated Block'
+      }
+    });
+
+    expect(response.statusCode).toBe(400);
+  });
+});
+
+describe('DELETE /projects/:projectId/blocks/:blockId', () => {
+  it('should delete a block', async () => {
+    (BlockService.deleteBlock as vi.Mock).mockResolvedValue(undefined);
+
+    const response = await app.inject({
+      method: 'DELETE',
+      url: '/projects/123/blocks/1'
+    });
+
+    expect(response.statusCode).toBe(204);
+  });
+
+  it('should handle validation errors', async () => {
+    const response = await app.inject({
+      method: 'DELETE',
+      url: '/projects/123/blocks/invalid-id'
+    });
+
+    expect(response.statusCode).toBe(400);
+  });
+});
+
+describe('POST /projects/:projectId/blocks/:blockId/insert', () => {
+  it('should insert a block instance', async () => {
+    const mockInstance = { id: '1', blockId: '1', position_x: 0, position_y: 0 };
+    (BlockService.insertBlockInstance as vi.Mock).mockResolvedValue(mockInstance);
+
+    const response = await app.inject({
+      method: 'POST',
+      url: '/projects/123/blocks/1/insert',
+      payload: {
+        position_x: 0,
+        position_y: 0
+      }
+    });
+
+    expect(response.statusCode).toBe(201);
+    expect(JSON.parse(response.body)).toEqual(mockInstance);
+  });
+
+  it('should handle validation errors', async () => {
+    const response = await app.inject({
+      method: 'POST',
+      url: '/projects/123/blocks/1/insert',
+      payload: {
+        // position_x is missing
+        position_y: 0
+      }
+    });
+
+    expect(response.statusCode).toBe(400);
+  });
+});
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