ProductTest is fully working

Author: fracz

src/main/java/pl/edu/agh/mwo/invoice/product/Product.java

@@ -10,6 +10,12 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
+        if (name == null || name.isEmpty()) {
+            throw new IllegalArgumentException("Product name cannot be null and cannot be empty");
+        }
+        if (price == null || price.signum() == -1) {
+            throw new IllegalArgumentException("Price cannot be negative and null.");
+        }
         this.name = name;
         this.price = price;
         this.taxPercent = tax;
@@ -20,14 +26,14 @@ public String getName() {
     }
 
     public BigDecimal getPrice() {
-        return null;
+        return price;
     }
 
     public BigDecimal getTaxPercent() {
-        return null;
+        return taxPercent;
     }
 
     public BigDecimal getPriceWithTax() {
-        return null;
+        return this.price.multiply(this.taxPercent).add(this.price);
     }
 }