diff --git a/src/server/sse.test.ts b/src/server/sse.test.ts
new file mode 100644
index 00000000..28474bad
--- /dev/null
+++ b/src/server/sse.test.ts
@@ -0,0 +1,109 @@
+import http from 'http'; 
+import { jest } from '@jest/globals';
+import { SSEServerTransport } from './sse.js'; 
+
+const createMockResponse = () => {
+  const res = {
+    writeHead: jest.fn<http.ServerResponse['writeHead']>(),
+    write: jest.fn<http.ServerResponse['write']>().mockReturnValue(true),
+    on: jest.fn<http.ServerResponse['on']>(),
+  };
+  res.writeHead.mockReturnThis();
+  res.on.mockReturnThis();
+  
+  return res as unknown as http.ServerResponse;
+};
+
+describe('SSEServerTransport', () => {
+  describe('start method', () => { 
+    it('should correctly append sessionId to a simple relative endpoint', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = '/messages';
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /messages?sessionId=${expectedSessionId}\n\n`
+      );
+    });
+
+    it('should correctly append sessionId to an endpoint with existing query parameters', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = '/messages?foo=bar&baz=qux';
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /messages?foo=bar&baz=qux&sessionId=${expectedSessionId}\n\n`
+      );
+    });
+
+    it('should correctly append sessionId to an endpoint with a hash fragment', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = '/messages#section1';
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /messages?sessionId=${expectedSessionId}#section1\n\n`
+      );
+    });
+
+    it('should correctly append sessionId to an endpoint with query parameters and a hash fragment', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = '/messages?key=value#section2';
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /messages?key=value&sessionId=${expectedSessionId}#section2\n\n`
+      );
+    });
+
+    it('should correctly handle the root path endpoint "/"', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = '/';
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /?sessionId=${expectedSessionId}\n\n`
+      );
+    });
+
+    it('should correctly handle an empty string endpoint ""', async () => { 
+      const mockRes = createMockResponse();
+      const endpoint = ''; 
+      const transport = new SSEServerTransport(endpoint, mockRes);
+      const expectedSessionId = (transport as any)._sessionId;
+
+      await transport.start();
+
+      expect(mockRes.writeHead).toHaveBeenCalledWith(200, expect.any(Object));
+      expect(mockRes.write).toHaveBeenCalledTimes(1);
+      expect(mockRes.write).toHaveBeenCalledWith(
+        `event: endpoint\ndata: /?sessionId=${expectedSessionId}\n\n`
+      );
+    });
+  });
+});