test(repo): ensure CHANGELOG.md is valid

It is easy to forget to add the brackets when adding a new "Unreleased"
version. Add a simple test to validate this.

Also fix a small issue the test caught.

Signed-off-by: Pablo Barbáchano <pablob@amazon.com>

CHANGELOG.md

@@ -1052,7 +1052,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   and to run as a daemon.
 - Enabled PATCH operations on `/drives` resources.
 
-## Changed
+### Changed
 
 - The microVM `id` supplied to the jailer may now contain alphanumeric
   characters and hyphens, up to a maximum length of 64 characters.

tests/integration_tests/style/test_repo.py

@@ -3,6 +3,7 @@
 
 """Tests enforcing git repository structure"""
 
+import re
 import subprocess
 from pathlib import Path
 
@@ -34,3 +35,25 @@ def test_repo_validate_yaml():
         if str(path).startswith("../build/"):
             continue
         yaml.safe_load(path.open(encoding="utf-8"))
+
+
+def test_repo_validate_changelog():
+    """Make sure the CHANGELOG.md file follows the Keep a Changelog format"""
+
+    changelog_path = Path("../CHANGELOG.md")
+    changelog = changelog_path.read_text(encoding="utf-8").splitlines()
+    errors = []
+    for lineno, line in enumerate(changelog, start=1):
+        if line.startswith("## "):
+            if not re.match(r"^## \[.+\]$", line):
+                msg = "Level 2 headings (versions) should be wrapped in []"
+                errors.append((lineno, msg, line))
+        if line.startswith("### "):
+            if not re.match(r"^### (Added|Changed|Deprecated|Removed|Fixed)$", line):
+                msg = "Unknown Level 3 heading"
+                errors.append((lineno, msg, line))
+
+    for lineno, msg, line in errors:
+        print(msg)
+        print(f"\t{lineno}:{line}")
+    assert len(errors) == 0