test: add roundtrip consistency tests

__tests__/roundtrip.spec.ts

@@ -0,0 +1,70 @@
+import { parseMd, revertMdAstNode } from './helpers';
+
+function stripPosition(node: any): any {
+  if (node === null || node === undefined) {
+    return node;
+  }
+  if (Array.isArray(node)) {
+    return node.map(stripPosition);
+  }
+  if (typeof node === 'object') {
+    const result: any = {};
+    for (const key of Object.keys(node)) {
+      if (key === 'position') {
+        continue;
+      }
+      result[key] = stripPosition(node[key]);
+    }
+    return result;
+  }
+  return node;
+}
+
+function assertRoundtrip(input: string) {
+  const ast1 = parseMd(input);
+  const md = revertMdAstNode(ast1);
+  const ast2 = parseMd(md);
+  expect(stripPosition(ast1)).toEqual(stripPosition(ast2));
+}
+
+describe('roundtrip consistency (parse → stringify → parse)', () => {
+  test('basic markdown (heading, paragraph, list)', () => {
+    assertRoundtrip('# Hello\n\nParagraph text.\n\n- item1\n- item2');
+  });
+
+  test('GFM table', () => {
+    assertRoundtrip('| a | b |\n|---|---|\n| 1 | 2 |');
+  });
+
+  test('GFM task list', () => {
+    assertRoundtrip('- [x] done\n- [ ] todo');
+  });
+
+  test('GFM strikethrough', () => {
+    assertRoundtrip('~deleted text~');
+  });
+
+  test('frontmatter', () => {
+    assertRoundtrip('---\ntitle: test\n---\n\nContent');
+  });
+
+  test('block math', () => {
+    assertRoundtrip('$$\nx^2\n$$');
+  });
+
+  test('inline math', () => {
+    assertRoundtrip('Text $x^2$ here');
+  });
+
+  test('container directive', () => {
+    assertRoundtrip(':::note\ncontent\n:::');
+  });
+
+  test('leaf directive', () => {
+    assertRoundtrip('::warning[content]');
+  });
+
+  test('mixed content', () => {
+    assertRoundtrip('# Title\n\nText with $math$ and ~~strike~~.\n\n| col1 | col2 |\n|------|------|\n| a    | b    |\n\n:::note\nDirective content\n:::');
+  });
+});