mathtool2/test/expr_parse_test.dart

// 粘贴用的解析器：把 Symja 文本转回节点树。
//
// 重点是**往返一致**：复制出来的东西粘回去应当还是同一个表达式；
// 以及**不认识就报错**，绝不猜着解析（猜错等于给用户一个算错的答案）。
import 'package:flutter_test/flutter_test.dart';

import 'package:cal/expr_node.dart';
import 'package:cal/expr_parse.dart';

/// 解析再序列化，应当和输入一模一样。
String rt(String s) => symjaOf(parseSymjaExpr(s));

void main() {
  group('基本往返', () {
    test('数字与四则', () {
      expect(rt('2'), '2');
      expect(rt('2+3'), '2+3');
      expect(rt('2x+1'), '2x+1');
      expect(rt('2*x+1'), '2*x+1');
      expect(rt('2.5'), '2.5');
    });

    test('函数调用', () {
      expect(rt('Sin[x]'), 'Sin[x]');
      expect(rt('Log[2x+1]'), 'Log[2x+1]');
      expect(rt('Integrate[x^2, x]'), 'Integrate[x^2, x]');
      expect(rt('Sin[]'), 'Sin[]');
    });

    test('幂与分式做成结构（要竖排/上标显示）', () {
      final doc = parseSymjaExpr('x^2');
      expect(doc.children.single, isA<PowNode>());
      final frac = parseSymjaExpr('1/3');
      expect(frac.children.single, isA<FracNode>());
    });

    test('分式分母是复合表达式时序列化补括号', () {
      expect(rt('1/(x+1)'), '1/(x+1)');
    });

    test('括号与花括号', () {
      expect(rt('(x+1)'), '(x+1)');
      expect(rt('2(x+1)'), '2(x+1)');  // 并置乘法原样保留，Symja 认这个写法
      expect(rt('{n, 1, Infinity}'), '{n, 1, Infinity}');
      expect(rt('Sum[f, {n, 1, Infinity}]'), 'Sum[f, {n, 1, Infinity}]');
    });

    test('空槽写成 Null，解析回来还是空槽', () {
      final t = parseSymjaExpr('Integrate[Null, x]');
      final op = t.children.single as BigOpNode;
      expect(op.body.isEmpty, isTrue);
      expect(symjaOf(t), 'Integrate[Null, x]');
    });

    test('定积分/求和/极限认成大运算符并能往返', () {
      final def = parseSymjaExpr('Integrate[x^2, {x, 0, 1}]');
      expect(def.children.single, isA<BigOpNode>());
      final op = def.children.single as BigOpNode;
      expect(op.kind, 'Integrate');
      expect(op.lower.isEmpty, isFalse);
      expect(op.upper.isEmpty, isFalse);
      expect(symjaOf(def), 'Integrate[x^2, {x, 0, 1}]');

      expect(symjaOf(parseSymjaExpr('Sum[f, {n, 1, Infinity}]')),
          'Sum[f, {n, 1, Infinity}]');
      expect(symjaOf(parseSymjaExpr('Product[f, {n, 1, m}]')),
          'Product[f, {n, 1, m}]');
      expect(symjaOf(parseSymjaExpr('Limit[Sin[x]/x, x -> 0]')),
          'Limit[Sin[x]/x, x -> 0]');
    });
  });

  group('运算符与词法', () {
    test('多字符运算符', () {
      expect(rt('x->0'), 'x->0');
      expect(rt('x^2-1==0'), 'x^2-1==0');
      expect(rt('f[x_]:=x^2'), 'f[x_]:=x^2');
    });

    test('一元负号', () {
      expect(rt('-x'), '-x');
      expect(rt('-1/2'), '-1/2');
    });

    test('科学计数法不能被拆成并置乘法', () {
      expect(rt('1e-3'), '1e-3');
      expect(rt('2.5E10'), '2.5E10');
    });

    test(r'标识符里的下划线和 $', () {
      expect(rt('x_'), 'x_');
      expect(rt(r'$ans'), r'$ans');
    });

    test('空白随便加', () {
      expect(rt('  2  x  +  1 '), '2x+1');
    });
  });

  group('不认识就报错，不猜', () {
    void bad(String s) {
      expect(() => parseSymjaExpr(s), throwsA(isA<ExprParseException>()),
          reason: '「$s」应当解析失败');
    }

    test('不支持的运算符', () {
      bad('a@b');
      bad('a&b');
      bad('x;;y');
      bad('a//b');
    });

    test('括号不配平', () {
      bad('(x+1');
      bad('Sin[x');
      bad('Abs[x]]');
    });

    test('多余的尾巴', () {
      bad('x y z ]');
      bad('1+2)');
    });

    test('空串', () {
      bad('');
    });

    test('报错信息带位置', () {
      try {
        parseSymjaExpr('x@y');
        fail('应当抛异常');
      } on ExprParseException catch (e) {
        expect(e.position, 1);
        expect(e.toString(), contains('第 2 个字符'));
      }
    });
  });
}