feat(options): add optional Options arguments to New() function (#14)

Enables simpler creation of custom *Golden instances, as you can just pass in the custom values to New(), rather than modifying fields after increating the Golden instance.

options_test.go

@@ -0,0 +1,58 @@
+package golden
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWithDirMode(t *testing.T) {
+	customMode := os.FileMode(0o700)
+	g := &Golden{}
+
+	opt := WithDirMode(customMode)
+	opt(g)
+
+	assert.Equal(t, customMode, g.DirMode)
+}
+
+func TestWithFileMode(t *testing.T) {
+	customMode := os.FileMode(0o600)
+	g := &Golden{}
+
+	opt := WithFileMode(customMode)
+	opt(g)
+
+	assert.Equal(t, customMode, g.FileMode)
+}
+
+func TestWithSuffix(t *testing.T) {
+	customSuffix := ".custom"
+	g := &Golden{}
+
+	opt := WithSuffix(customSuffix)
+	opt(g)
+
+	assert.Equal(t, customSuffix, g.Suffix)
+}
+
+func TestWithDirname(t *testing.T) {
+	customDirname := "custom-testdata"
+	g := &Golden{}
+
+	opt := WithDirname(customDirname)
+	opt(g)
+
+	assert.Equal(t, customDirname, g.Dirname)
+}
+
+func TestWithUpdateFunc(t *testing.T) {
+	customUpdateFunc := func() bool { return true }
+	g := &Golden{}
+
+	opt := WithUpdateFunc(customUpdateFunc)
+	opt(g)
+
+	assertSameFunc(t, customUpdateFunc, g.UpdateFunc)
+}