ProductTest is fully working

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

@@ -10,24 +10,34 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
-        this.name = name;
+        if (name == null || name.equals("")) {
+        	throw new IllegalArgumentException(
+        		"You cannot create products with null or empty name."
+			);
+        }
+        if (price == null || price.signum() == -1) {
+        	throw new IllegalArgumentException(
+        		"You cannot create products with null or negative price."
+			);
+        }
+    	this.name = name;
         this.price = price;
         this.taxPercent = tax;
     }
 
     public String getName() {
-        return null;
+        return this.name;
     }
 
     public BigDecimal getPrice() {
-        return null;
-    }
+		return price;
+	}
 
-    public BigDecimal getTaxPercent() {
-        return null;
-    }
+	public BigDecimal getTaxPercent() {
+		return taxPercent;
+	}
 
-    public BigDecimal getPriceWithTax() {
-        return null;
+	public BigDecimal getPriceWithTax() {
+        return this.price.multiply(this.taxPercent).add(this.price);
     }
 }