[#1364] cmd/common: Add tests for CreateViper and ReloadViper

Add tests for `CreateViper` and `ReloadViper` to ensure that no extra
files, except *.yaml, *.yml, *.json, are loaded from config directory.

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

pkg/util/config/test/generate.go

@@ -0,0 +1,58 @@
+package configtest
+
+import (
+	"crypto/rand"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type MarshalFunc = func(any) ([]byte, error)
+
+type ConfigFile struct {
+	filename string
+	content  map[string]any
+	marshal  func(any) ([]byte, error)
+}
+
+type DummyFile struct {
+	filename string
+	size     int
+}
+
+func NewConfigFile(filename string, content map[string]any, marshal MarshalFunc) ConfigFile {
+	return ConfigFile{
+		filename: filename,
+		content:  content,
+		marshal:  marshal,
+	}
+}
+
+func NewDummyFile(filename string, size int) DummyFile {
+	return DummyFile{
+		filename: filename,
+		size:     size,
+	}
+}
+
+func PrepareConfigFiles(t *testing.T, dir string, files []ConfigFile) {
+	for _, file := range files {
+		data, err := file.marshal(file.content)
+		require.NoError(t, err)
+
+		err = os.WriteFile(path.Join(dir, file.filename), data, 0o600)
+		require.NoError(t, err)
+	}
+}
+
+func PrepareDummyFiles(t *testing.T, dir string, files []DummyFile) {
+	for _, file := range files {
+		data := make([]byte, file.size)
+		_, _ = rand.Read(data)
+
+		err := os.WriteFile(path.Join(dir, file.filename), data, 0o600)
+		require.NoError(t, err)
+	}
+}