Fix configuration validation

Due to my over-cleverness and lack of use a pointer in the right spot
the configuration file was not capable of setting any actual settings.

I use the defaults in my test environment so ... there you go. There are
some basic tests now.

Signed-off-by: Erik Hollensbe <github@hollensbe.org>

config/config.go

@@ -32,15 +32,15 @@ type Config struct {
 }
 
 // Empty is a config that has all the defaults configured; usually for testing.
-func Empty() Config {
-	c := Config{}
+func Empty() *Config {
+	c := &Config{}
 	c.validateAndFix()
 	return c
 }
 
 // Parse parses the configuration in the file and returns it.
-func Parse(filename string) (Config, error) {
-	var config Config
+func Parse(filename string) (*Config, error) {
+	config := &Config{}
 
 	content, err := ioutil.ReadFile(filename)
 	if err != nil {

config/config_test.go

@@ -0,0 +1,41 @@
+package config
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestConfigDefaults(t *testing.T) {
+	t.Run("empty equals the defaults", func(t *testing.T) {
+		c := Empty()
+		if err := c.validateAndFix(); err != nil {
+			t.Fatalf("empty configuration errored out on validation: %v", err)
+		}
+
+		c2 := Empty()
+		if !reflect.DeepEqual(c, c2) {
+			t.Fatal("empty is not equal to the empty after validation")
+		}
+
+		c3 := &Config{}
+		if err := c3.validateAndFix(); err != nil {
+			t.Fatal("empty configuration did not validate properly")
+		}
+
+		if !reflect.DeepEqual(c2, c3) {
+			t.Fatal("empty, validated configuration was not equal to empty configuration")
+		}
+	})
+
+	t.Run("defaults are overridable before validation", func(t *testing.T) {
+		c := Empty()
+		c.Domain = "home"
+		if err := c.validateAndFix(); err != nil {
+			t.Fatalf("errored out changing the hostname pre-validation: %v", err)
+		}
+
+		if c.Domain != "home" {
+			t.Fatalf("previously set value was not preserved post-validation")
+		}
+	})
+}

service/service.go

@@ -18,7 +18,7 @@ import (
 
 // Service is the encapsulation of a fully composed service.
 type Service struct {
-	config  config.Config
+	config  *config.Config
 	appName string
 	grpcS   *grpc.Server
 	l       net.Listener
@@ -43,7 +43,7 @@ func (s *Service) InstallSignalHandler() {
 }
 
 // New constructs a new service from a config.Config
-func New(name string, c config.Config) (*Service, error) {
+func New(name string, c *config.Config) (*Service, error) {
 	db, err := dnsdb.New(c.DBFile)
 	if err != nil {
 		return nil, errors.Wrap(err, "could not open database")