Fix InitWithReset - rely on previously updated flags (#7598)

* Fix initWithReset to use previously set configuration

* further cleanup

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

shared/featureconfig/config.go

@@ -94,8 +94,14 @@ func Init(c *Flags) {
 
 // InitWithReset sets the global config and returns function that is used to reset configuration.
 func InitWithReset(c *Flags) func() {
+	var prevConfig Flags
+	if featureConfig != nil {
+		prevConfig = *featureConfig
+	} else {
+		prevConfig = Flags{}
+	}
 	resetFunc := func() {
-		Init(&Flags{})
+		Init(&prevConfig)
 	}
 	Init(c)
 	return resetFunc

shared/featureconfig/config_test.go

@@ -9,6 +9,7 @@ import (
 )
 
 func TestInitFeatureConfig(t *testing.T) {
+	defer Init(&Flags{})
 	cfg := &Flags{
 		MedallaTestnet: true,
 	}
@@ -21,6 +22,27 @@ func TestInitFeatureConfig(t *testing.T) {
 	Init(cfg)
 }
 
+func TestInitWithReset(t *testing.T) {
+	defer Init(&Flags{})
+	Init(&Flags{
+		OnyxTestnet: true,
+	})
+	assert.Equal(t, false, Get().AltonaTestnet)
+	assert.Equal(t, true, Get().OnyxTestnet)
+
+	// Overwrite previously set value (value that didn't come by default).
+	resetCfg := InitWithReset(&Flags{
+		OnyxTestnet: false,
+	})
+	assert.Equal(t, false, Get().AltonaTestnet)
+	assert.Equal(t, false, Get().OnyxTestnet)
+
+	// Reset must get to previously set configuration (not to default config values).
+	resetCfg()
+	assert.Equal(t, false, Get().AltonaTestnet)
+	assert.Equal(t, true, Get().OnyxTestnet)
+}
+
 func TestConfigureBeaconConfig(t *testing.T) {
 	app := cli.App{}
 	set := flag.NewFlagSet("test", 0)