single-src: introduce calculatedProduction getter

Author: kaiosilveira

src/single-source/index.js

@@ -8,6 +8,10 @@ export class ProductionPlan {
     return this._production;
   }
 
+  get calculatedProduction() {
+    return this._adjustments.reduce((sum, a) => sum + a.amount, 0);
+  }
+
   applyAdjustment(anAdjustment) {
     this._adjustments.push(anAdjustment);
     this._production += anAdjustment.amount;