order: Add Side type MarshalJSON method (#1726)

* Add side MarshalJSON

* glorious: nits

* more removal

* Update exchanges/order/order_test.go

Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

---------

Co-authored-by: Ryan O'Hara-Reid <ryan.oharareid@thrasher.io>
Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

exchanges/order/order_test.go

@@ -2123,6 +2123,16 @@ func TestSideUnmarshal(t *testing.T) {
 	assert.ErrorAs(t, s.UnmarshalJSON([]byte(`14`)), &jErr, "non-string valid json is rejected")
 }
 
+func TestSideMarshalJSON(t *testing.T) {
+	t.Parallel()
+	b, err := Buy.MarshalJSON()
+	assert.NoError(t, err)
+	assert.Equal(t, `"BUY"`, string(b))
+	b, err = UnknownSide.MarshalJSON()
+	assert.NoError(t, err)
+	assert.Equal(t, `"UNKNOWN"`, string(b))
+}
+
 func TestGetTradeAmount(t *testing.T) {
 	t.Parallel()
 	var s *Submit

exchanges/order/orders.go

@@ -1115,6 +1115,11 @@ func (s *Side) UnmarshalJSON(data []byte) (err error) {
 	return
 }
 
+// MarshalJSON returns the JSON-encoded order side
+func (s Side) MarshalJSON() ([]byte, error) {
+	return []byte(`"` + s.String() + `"`), nil
+}
+
 // StringToOrderType for converting case insensitive order type
 // and returning a real Type
 func StringToOrderType(oType string) (Type, error) {