feat(release): generate the GitHub release body from the changelog (#2987)

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

cmd/release/notes_test.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/Masterminds/semver/v3"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestChangelogSection(t *testing.T) {
+	t.Parallel()
+
+	const changelog = `# Changelog
+
+## v3.53.1 - 2026-08-18
+
+### 🚀 Features
+
+- Something new (#1 by @someone).
+
+### 🐛 Fixes
+
+- Something fixed (#2 by @someone).
+
+## v3.53.10 - 2026-08-17
+
+- An entry of a version whose heading starts with "## v3.53.1".
+
+## v3.5.0 - 2026-01-01
+
+- An older entry.
+`
+
+	tests := []struct {
+		name     string
+		version  string
+		expected string
+	}{
+		{
+			name:    "section with sub-headings",
+			version: "3.53.1",
+			expected: `### 🚀 Features
+
+- Something new (#1 by @someone).
+
+### 🐛 Fixes
+
+- Something fixed (#2 by @someone).`,
+		},
+		{
+			name:     "last section of the file",
+			version:  "3.5.0",
+			expected: "- An older entry.",
+		},
+		{
+			// A patch release may ship without changelog entries.
+			name:     "missing section",
+			version:  "3.53.2",
+			expected: "",
+		},
+		{
+			name:     "heading of another version starts with this one",
+			version:  "3.53.10",
+			expected: `- An entry of a version whose heading starts with "## v3.53.1".`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			version := semver.MustParse(test.version)
+			assert.Equal(t, test.expected, changelogSection(changelog, version))
+		})
+	}
+}