add config validate tests

config.go

@@ -33,7 +33,7 @@ func (cfg *config) parseFlags() {
 }
 
 // ValidateFlags custom validation for flags aside from pflag provided
-func (cfg *config) validateFlags() error {
+func (cfg *config) validate() error {
 	if cfg.logFormat != "text" && cfg.logFormat != "json" {
 		return fmt.Errorf("unsupported log format: %s", cfg.logFormat)
 	}

config_test.go

+package main
+
+import (
+	"testing"
+)
+
+func TestValidateFlags(t *testing.T) {
+	cfg := newConfig()
+	cfg.logFormat = "test"
+	if err := cfg.validate(); err == nil {
+		t.Errorf("unsupported log format should fail: %s", cfg.logFormat)
+	}
+	cfg.logFormat = ""
+	if err := cfg.validate(); err == nil {
+		t.Errorf("unsupported log format should fail: %s", cfg.logFormat)
+	}
+	for _, format := range []string{"text", "json"} {
+		cfg.logFormat = format
+		if err := cfg.validate(); err != nil {
+			t.Errorf("supported log format: %s should not fail", format)
+		}
+	}
+}

main.go

@@ -16,8 +16,8 @@ import (
 func main() {
 	cfg := newConfig()
 	cfg.parseFlags()
-	if err := cfg.validateFlags(); err != nil {
-		log.Errorf("flag validation failed: %v", err)
+	if err := cfg.validate(); err != nil {
+		log.Errorf("config validation failed: %v", err)
 	}
 
 	if cfg.logFormat == "json" {