Add InvoiceTestDataBuilder for creating test data for Invoice class

java/TODO.md

@@ -5,7 +5,7 @@ We will be using the mikado method to incrementally create the test data builder
 Indentation represents dependencies, and should be done first
 
 - [ ] Add a test to highlight the issue in Invoice, using the test data builder pattern
-  - [ ] Create a test data builder for the Invoice class
+  - [x] Create a test data builder for the Invoice class
     - [x] Create a test data builder for the PurchaseBook class
       - [x] Create a test data builder for the Novel class
         - [x] Create test data builder for Author

java/src/test/java/com/murex/tbw/purchase/InvoiceTestDataBuilder.java

@@ -0,0 +1,36 @@
+package com.murex.tbw.purchase;
+
+import com.murex.tbw.domain.country.Country;
+import com.murex.tbw.domain.country.TestCountries;
+
+import java.util.ArrayList;
+
+public class InvoiceTestDataBuilder {
+
+    private final ArrayList<PurchasedBook> purchasedBooks = new ArrayList<>();
+    private Country country = TestCountries.USA;
+
+    public static InvoiceTestDataBuilder anInvoice() {
+        return new InvoiceTestDataBuilder();
+    }
+
+    public InvoiceTestDataBuilder with(PurchasedBookTestDataBuilder... purchasedBookTestDataBuilders) {
+        for (PurchasedBookTestDataBuilder purchasedBookTestDataBuilder : purchasedBookTestDataBuilders) {
+            purchasedBooks.add(purchasedBookTestDataBuilder.build());
+        }
+        return this;
+    }
+
+    public InvoiceTestDataBuilder sentTo(Country country) {
+        this.country = country;
+        return this;
+    }
+
+    public Invoice build() {
+        Invoice invoice = new Invoice("John Doe", this.country);
+        for (PurchasedBook purchasedBook : purchasedBooks) {
+            invoice.addPurchasedBook(purchasedBook);
+        }
+        return invoice;
+    }
+}