diff --git a/field-logic/src/lib/engine.test.ts b/field-logic/src/lib/engine.test.ts
index dcf3bb6..ad71923 100644
--- a/field-logic/src/lib/engine.test.ts
+++ b/field-logic/src/lib/engine.test.ts
@@ -1,98 +1,104 @@
-import { describe, it, expect, beforeEach } from 'vitest';
-import { SurveyEngine } from './SurveyEngine';
-import type { SurveyDefinition } from '../types/schema';
+import { describe, it, expect, beforeEach } from "vitest";
+import { SurveyEngine } from "./SurveyEngine";
+import type { SurveyDefinition } from "../types/schema";
 
 const mockSurvey: SurveyDefinition = {
-    meta: {
-        survey_id: "test_v1",
-        title: "Test Survey",
-        version: "1.0",
-        created_at: "2023-01-01"
+  meta: {
+    survey_id: "test_v1",
+    title: "Test Survey",
+    version: "1.0",
+    created_at: "2023-01-01",
+  },
+  config: {
+    allow_back_navigation: true,
+    save_progress_automatically: false,
+  },
+  nodes: [
+    {
+      id: "start",
+      type: "info",
+      content: { text: "Welcome" },
+      routing: { default: "q1" },
     },
-    config: {
-        allow_back_navigation: true,
-        save_progress_automatically: false
+    {
+      id: "q1",
+      type: "boolean",
+      content: { question: "Yes or No?" },
+      routing: {
+        rules: [
+          { operator: "equals", value: true, target: "q2_yes" },
+          { operator: "equals", value: false, target: "q2_no" },
+        ],
+        default: "end",
+      },
     },
-    nodes: [
-        {
-            id: "start",
-            type: "info",
-            content: { text: "Welcome" },
-            routing: { default: "q1" }
-        },
-        {
-            id: "q1",
-            type: "boolean",
-            content: { question: "Yes or No?" },
-            routing: {
-                rules: [
-                    { operator: "equals", value: true, target: "q2_yes" },
-                    { operator: "equals", value: false, target: "q2_no" }
-                ],
-                default: "end"
-            }
-        },
-        {
-            id: "q2_yes",
-            type: "text",
-            content: { question: "Why yes?" },
-            routing: { default: "end" }
-        },
-        {
-            id: "q2_no",
-            type: "text",
-            content: { question: "Why no?" },
-            routing: { default: "end" }
-        },
-        {
-            id: "end",
-            type: "summary",
-            content: { text: "Done" },
-            routing: { default: null }
-        }
-    ]
+    {
+      id: "q2_yes",
+      type: "text",
+      content: { question: "Why yes?" },
+      routing: { default: "end" },
+    },
+    {
+      id: "q2_no",
+      type: "text",
+      content: { question: "Why no?" },
+      routing: { default: "end" },
+    },
+    {
+      id: "end",
+      type: "summary",
+      content: { text: "Done" },
+      routing: { default: null },
+    },
+  ],
 };
 
-describe('SurveyEngine', () => {
-    let engine: SurveyEngine;
+describe("SurveyEngine", () => {
+  let engine: SurveyEngine;
+
+  beforeEach(() => {
+    engine = new SurveyEngine(mockSurvey, "test_session");
+  });
 
-    beforeEach(() => {
-        engine = new SurveyEngine(mockSurvey, 'test_session');
-    });
+  it("should start at the first node", () => {
+    const node = engine.start();
+    expect(node.id).toBe("start");
+  });
 
-    it('should start at the first node', () => {
-        const node = engine.start();
-        expect(node.id).toBe('start');
-    });
+  it("should navigate to next node via default route", () => {
+    engine.start();
+    const node = engine.submitAnswer(null); // 'info' type has no answer
+    expect(node?.id).toBe("q1");
+  });
 
-    it('should navigate to next node via default route', () => {
-        engine.start();
-        const node = engine.submitAnswer(null); // 'info' type has no answer
-        expect(node?.id).toBe('q1');
-    });
+  it("should handle boolean branching (true)", () => {
+    engine.start();
+    engine.submitAnswer(null); // move to q1
+    const node = engine.submitAnswer(true); // Answer true to q1
+    expect(node?.id).toBe("q2_yes");
+  });
 
-    it('should handle boolean branching (true)', () => {
-        engine.start();
-        engine.submitAnswer(null); // move to q1
-        const node = engine.submitAnswer(true); // Answer true to q1
-        expect(node?.id).toBe('q2_yes');
-    });
+  it("should handle boolean branching (false)", () => {
+    engine.start();
+    engine.submitAnswer(null); // move to q1
+    const node = engine.submitAnswer(false); // Answer false to q1
+    expect(node?.id).toBe("q2_no");
+  });
 
-    it('should handle boolean branching (false)', () => {
-        engine.start();
-        engine.submitAnswer(null); // move to q1
-        const node = engine.submitAnswer(false); // Answer false to q1
-        expect(node?.id).toBe('q2_no');
-    });
+  it("should record answers in session", () => {
+    engine.start();
+    engine.submitAnswer(null); // q1
+    engine.submitAnswer(true); // q2_yes
+    const session = engine.getSession();
 
-    it('should record answers in session', () => {
-        engine.start();
-        engine.submitAnswer(null); // q1
-        engine.submitAnswer(true); // q2_yes
-        const session = engine.getSession();
+    expect(session.responses["q1"]).toBe(true);
+    expect(session.visitedNodes).toContain("q1");
+    expect(session.visitedNodes).toContain("q2_yes");
+  });
 
-        expect(session.responses['q1']).toBe(true);
-        expect(session.visitedNodes).toContain('q1');
-        expect(session.visitedNodes).toContain('q2_yes');
-    });
+  it("should throw error if submitAnswer called before start", () => {
+    expect(() => engine.submitAnswer("some answer")).toThrow(
+      "Survey not active",
+    );
+  });
 });