fix rates

test/rate_test.dart

@@ -0,0 +1,33 @@
+import 'package:fcs/domain/entities/cargo_type.dart';
+import 'package:fcs/domain/entities/carton.dart';
+import 'package:fcs/domain/entities/discount_by_weight.dart';
+import 'package:fcs/domain/entities/rate.dart';
+import 'package:test/test.dart';
+
+@TestOn('vm')
+void main() {
+  var rate = Rate();
+  rate.discountByWeights = [
+    DiscountByWeight(weight: 25, discount: 0.25),
+    DiscountByWeight(weight: 50, discount: 0.5),
+  ];
+  rate.volumetricRatio = 166.36;
+  rate.diffDiscountWeight = 5;
+  rate.diffWeightRate = 1.5;
+
+  test('Calculate carton price 1', () {
+    var ct = CargoType(name: "General", weight: 10, rate: 6);
+    var carton = Carton(cargoTypes: [ct], length: 15, width: 15, height: 15);
+    expect(carton.calAmount(rate), equals(67.50));
+  });
+  test('Calculate carton price 2', () {
+    var ct = CargoType(name: "General", weight: 10, rate: 6);
+    var carton = Carton(cargoTypes: [ct], length: 10, width: 10, height: 10);
+    expect(carton.calAmount(rate), equals(60));
+  });
+    test('Calculate carton price 3', () {
+    var ct = CargoType(name: "General", weight: 10, rate: 6);
+    var carton = Carton(cargoTypes: [ct], length: 15, width: 15, height: 10);
+    expect(carton.calAmount(rate), equals(60));
+  });
+}