test: Enhance Coverage + CI (#1055)

Reviewed-on: https://gitea.com/gitea/runner/pulls/1055
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>

internal/pkg/config/registration_test.go

@@ -0,0 +1,51 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSaveAndLoadRegistration(t *testing.T) {
+	file := filepath.Join(t.TempDir(), ".runner")
+
+	reg := &Registration{
+		ID:        42,
+		UUID:      "the-uuid",
+		Name:      "runner",
+		Token:     "the-token",
+		Address:   "http://localhost:3000",
+		Labels:    []string{"ubuntu:host", "ubuntu:docker://node:18"},
+		Ephemeral: true,
+	}
+
+	require.NoError(t, SaveRegistration(file, reg))
+	// SaveRegistration stamps the warning onto the in-memory struct
+	require.Equal(t, registrationWarning, reg.Warning)
+
+	loaded, err := LoadRegistration(file)
+	require.NoError(t, err)
+
+	// the warning is intentionally cleared on load
+	require.Empty(t, loaded.Warning)
+	loaded.Warning = reg.Warning
+	require.Equal(t, reg, loaded)
+}
+
+func TestLoadRegistrationMissingFile(t *testing.T) {
+	_, err := LoadRegistration(filepath.Join(t.TempDir(), "does-not-exist"))
+	require.Error(t, err)
+}
+
+func TestLoadRegistrationInvalidJSON(t *testing.T) {
+	file := filepath.Join(t.TempDir(), ".runner")
+	require.NoError(t, os.WriteFile(file, []byte("not json"), 0o600))
+
+	_, err := LoadRegistration(file)
+	require.Error(t, err)
+}