괄호 안의 항을 2, 3, 4 항으로 설정하는 기능 추가

lib/engine/parenthesis-sign.test.ts

@@ -63,8 +63,19 @@ describe("parenthesis sign problem engine", () => {
     expect(keys.size).toBe(10);
   });
 
+  it("generates the selected number of terms inside parentheses", () => {
+    const problem = generateProblem(4);
+
+    expect(problem.terms).toHaveLength(4);
+    expect(problem.operators).toHaveLength(3);
+    expect(problem.distributedTerms).toHaveLength(4);
+    expect(
+      gradeAnswer(problem, { terms: problem.distributedTerms }).correct,
+    ).toBe(true);
+  });
+
   it("rejects impossible session sizes", () => {
     expect(() => generateSession(0)).toThrow();
-    expect(() => generateSession(145)).toThrow();
+    expect(() => generateSession(1297)).toThrow();
   });
 });