괄호 안의 항을 2, 3, 4 항으로 설정하는 기능 추가

lib/engine/variable-parenthesis.test.ts

@@ -10,7 +10,7 @@ import type { VariableParenthesisProblem } from "./variable-types";
 
 function findCorrectChoiceIds(problem: VariableParenthesisProblem) {
   return problem.correctTerms.map((term, index) => {
-    const choices = problem.choices[index as 0 | 1];
+    const choices = problem.choices[index];
     const choice = choices.find(
       (item) =>
         item.coefficient === term.coefficient && item.variable === term.variable,
@@ -19,7 +19,7 @@ function findCorrectChoiceIds(problem: VariableParenthesisProblem) {
     if (!choice) throw new Error("correct choice not found.");
 
     return choice.id;
-  }) as [string, string];
+  });
 }
 
 describe("variable parenthesis engine", () => {
@@ -97,6 +97,21 @@ describe("variable parenthesis engine", () => {
     expect(keys.size).toBe(10);
   });
 
+  it("generates the selected number of variable choices", () => {
+    const problem = generateVariableParenthesisProblem(4);
+
+    expect(problem.terms).toHaveLength(4);
+    expect(problem.operators).toHaveLength(3);
+    expect(problem.correctTerms).toHaveLength(4);
+    expect(problem.choices).toHaveLength(4);
+    expect(problem.terms.filter((term) => term.kind === "variable")).toHaveLength(1);
+    expect(
+      gradeVariableParenthesisAnswer(problem, {
+        selectedChoiceIds: findCorrectChoiceIds(problem),
+      }).correct,
+    ).toBe(true);
+  });
+
   it("formats expressions with variable terms", () => {
     expect(
       formatVariableExpressionLatex([