match release-plan test for Changelog header

bin/bin.test.js

@@ -72,6 +72,18 @@ describe('main binary', function () {
     );
   });
 
+  it('does not modify if an existing prefix exists anywhere on the line and has different casing in CHANGELOG.md', async function () {
+    project.files['CHANGELOG.md'] =
+      `# the most mighty CHANgELOG you have ever seen\n\n## v1.2.0\n* Foo bar`;
+    project.writeSync();
+
+    await exec(['--no-install', '--no-label-updates']);
+
+    expect(fs.readFileSync('CHANGELOG.md', { encoding: 'utf8' })).toBe(
+      '# the most mighty CHANgELOG you have ever seen\n\n## v1.2.0\n* Foo bar'
+    );
+  });
+
   describe('package.json', function () {
     it('adds repository info when discoverable from `.git/config`', async function () {
       project.files['.git'] = {

bin/release-plan-setup.js

@@ -5,7 +5,6 @@ import util from 'util';
 import { execa } from 'execa';
 import sortPackageJson from 'sort-package-json';
 import gitconfiglocal from 'gitconfiglocal';
-import { fromMarkdown } from 'mdast-util-from-markdown';
 import findRepoURL from '../lib/findRepoUrl.js';
 import getDependencyRange from '../lib/getDependencyRange.js';
 import ejs from 'ejs';
@@ -158,13 +157,11 @@ try {
   }
 
   if (hasChangelog && !labelsOnly) {
-    let changelogContent = fs.readFileSync('CHANGELOG.md', { encoding: 'utf8' });
-    let ast = fromMarkdown(changelogContent);
+    let changelogContent = fs.readFileSync('CHANGELOG.md', { encoding: 'utf8' }).split('\n');
+    const changelogPreamblePattern = /#.*Changelog.*$/i;
 
-    let hasH1 = ast.children.find((it) => it.type === 'heading' && it.depth === 1);
-
-    if (!hasH1) {
-      fs.writeFileSync('CHANGELOG.md', `# Changelog\n\n${changelogContent}`, {
+    if (!changelogPreamblePattern.test(changelogContent[0])) {
+      fs.writeFileSync('CHANGELOG.md', `# Changelog\n\n${changelogContent.join('\n')}`, {
         encoding: 'utf8',
       });
     }

package.json

@@ -28,7 +28,6 @@
     "github-label-sync": "^2.3.1",
     "hosted-git-info": "^7.0.1",
     "lodash.template": "^4.5.0",
-    "mdast-util-from-markdown": "^2.0.0",
     "semver": "^7.3.5",
     "sort-package-json": "^2.6.0",
     "which": "^4.0.0"