Config: Refactor version packages (#1887)

* Config: Move config versions to separate pacakges

* Config: Move version tests to blackbox texts

* Config: Protect registerVersion from overflow

* Config: Protect against version already registered

config/versions/v0/v0.go

@@ -0,0 +1,19 @@
+package v0
+
+import (
+	"context"
+)
+
+// Version is a baseline version with no changes, so we can downgrade back to nothing
+// It does not implement any upgrade interfaces
+type Version struct{}
+
+// UpgradeConfig is an empty stub
+func (*Version) UpgradeConfig(_ context.Context, j []byte) ([]byte, error) {
+	return j, nil
+}
+
+// DowngradeConfig is an empty stub
+func (*Version) DowngradeConfig(_ context.Context, j []byte) ([]byte, error) {
+	return j, nil
+}

config/versions/v0/v0_test.go

@@ -0,0 +1,26 @@
+package v0_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	v0 "github.com/thrasher-corp/gocryptotrader/config/versions/v0"
+)
+
+func TestUpgradeConfig(t *testing.T) {
+	t.Parallel()
+	in := []byte(`{"untouched":true}`)
+	out, err := new(v0.Version).UpgradeConfig(context.Background(), in)
+	require.NoError(t, err)
+	assert.Equal(t, in, out)
+}
+
+func TestDowngradeConfig(t *testing.T) {
+	t.Parallel()
+	in := []byte(`{"untouched":true}`)
+	out, err := new(v0.Version).DowngradeConfig(context.Background(), in)
+	require.NoError(t, err)
+	assert.Equal(t, in, out)
+}