cmd/ctrld: honor configPath when writing config file

Updates #58

cmd/ctrld/cli.go

@@ -445,6 +445,8 @@ func initCLI() {
 func writeConfigFile() error {
 	if cfu := v.ConfigFileUsed(); cfu != "" {
 		defaultConfigFile = cfu
+	} else if configPath != "" {
+		defaultConfigFile = configPath
 	}
 	f, err := os.OpenFile(defaultConfigFile, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, os.FileMode(0o644))
 	if err != nil {

cmd/ctrld/cli_test.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_writeConfigFile(t *testing.T) {
+	tmpdir := t.TempDir()
+	// simulate --config CLI flag by setting configPath manually.
+	configPath = filepath.Join(tmpdir, "ctrld.toml")
+	_, err := os.Stat(configPath)
+	assert.True(t, os.IsNotExist(err))
+
+	assert.NoError(t, writeConfigFile())
+
+	_, err = os.Stat(configPath)
+	require.NoError(t, err)
+}