diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 56fe02359..30854f8f6 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -1,30 +1,39 @@
 package pl.edu.agh.mwo.invoice;
 
 import java.math.BigDecimal;
-import java.util.Collection;
+import java.util.LinkedHashMap;
+import java.util.Map;
 
 import pl.edu.agh.mwo.invoice.product.Product;
 
 public class Invoice {
-    private Collection<Product> products;
+    private Map<Product, Integer> products = new LinkedHashMap<>();
 
     public void addProduct(Product product) {
-        // TODO: implement
+        this.products.put(product, 1);
     }
 
     public void addProduct(Product product, Integer quantity) {
-        // TODO: implement
+    	this.products.put(product, quantity);
     }
 
-    public BigDecimal getSubtotal() {
-        return null;
+    public BigDecimal getSubtotal() {        
+    	BigDecimal sum = BigDecimal.ZERO;
+    	
+    	for (Product product : this.products.keySet()) {
+    		Integer quantity = this.products.get(product);
+    		sum = sum.add(product.getPrice().multiply(new BigDecimal(quantity)));
+    	}
+    	
+    	return sum;
     }
 
+       
     public BigDecimal getTax() {
-        return null;
+        return BigDecimal.ZERO;
     }
 
     public BigDecimal getTotal() {
-        return null;
+        return BigDecimal.ZERO;
     }
 }
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index 318de9ac9..6c1f7a789 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -10,24 +10,37 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
-        this.name = name;
+        if(name == null) {
+        	throw new IllegalArgumentException ("You cannot create product with null name");
+        }
+        if(name.equals("")) {
+        	throw new IllegalArgumentException ("You cannot create product with empty name");
+        }
+    	this.name = name;
+    	if(price == null) {
+        	throw new IllegalArgumentException ("You cannot create product with null price");
+        }
+    	if(price.signum() == -1) {
+        	throw new IllegalArgumentException ("You cannot create product with negative price");
+        }
         this.price = price;
+        
         this.taxPercent = tax;
     }
 
     public String getName() {
-        return null;
+        return this.name;
     }
 
     public BigDecimal getPrice() {
-        return null;
+        return this.price;
     }
 
     public BigDecimal getTaxPercent() {
-        return null;
+        return this.taxPercent;
     }
 
     public BigDecimal getPriceWithTax() {
-        return null;
+    	return this.price.multiply(this.taxPercent).add(this.price);
     }
 }
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
new file mode 100644
index 000000000..8dce08e28
--- /dev/null
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -0,0 +1,107 @@
+package pl.edu.agh.mwo.invoice;
+
+import java.math.BigDecimal;
+
+import org.hamcrest.Matchers;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import pl.edu.agh.mwo.invoice.Invoice;
+import pl.edu.agh.mwo.invoice.product.DairyProduct;
+import pl.edu.agh.mwo.invoice.product.OtherProduct;
+import pl.edu.agh.mwo.invoice.product.Product;
+import pl.edu.agh.mwo.invoice.product.TaxFreeProduct;
+
+public class InvoiceTest {
+    private Invoice invoice;
+
+    @Before
+    public void createEmptyInvoiceForTheTest() {
+        invoice = new Invoice();
+    }
+
+    @Test
+    public void testEmptyInvoiceHasEmptySubtotal() {
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getSubtotal()));
+    }
+
+    @Test
+    public void testEmptyInvoiceHasEmptyTaxAmount() {
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTax()));
+    }
+
+    @Test
+    public void testEmptyInvoiceHasEmptyTotal() {
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTotal()));
+    }
+
+    @Test
+    public void testInvoiceHasTheSameSubtotalAndTotalIfTaxIsZero() {
+        Product taxFreeProduct = new TaxFreeProduct("Warzywa", new BigDecimal("199.99"));
+        invoice.addProduct(taxFreeProduct);
+        Assert.assertThat(invoice.getTotal(), Matchers.comparesEqualTo(invoice.getSubtotal()));
+    }
+
+    @Test
+    public void testInvoiceHasProperSubtotalForManyProducts() {
+        invoice.addProduct(new TaxFreeProduct("Owoce", new BigDecimal("200")));
+        invoice.addProduct(new DairyProduct("Maslanka", new BigDecimal("100")));
+        invoice.addProduct(new OtherProduct("Wino", new BigDecimal("10")));
+        Assert.assertThat(new BigDecimal("310"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+    }
+
+    @Test
+    public void testInvoiceHasProperTaxValueForManyProduct() {
+        // tax: 0
+        invoice.addProduct(new TaxFreeProduct("Pampersy", new BigDecimal("200")));
+        // tax: 8
+        invoice.addProduct(new DairyProduct("Kefir", new BigDecimal("100")));
+        // tax: 2.30
+        invoice.addProduct(new OtherProduct("Piwko", new BigDecimal("10")));
+        Assert.assertThat(new BigDecimal("10.30"), Matchers.comparesEqualTo(invoice.getTax()));
+    }
+
+    @Test
+    public void testInvoiceHasProperTotalValueForManyProduct() {
+        // price with tax: 200
+        invoice.addProduct(new TaxFreeProduct("Maskotki", new BigDecimal("200")));
+        // price with tax: 108
+        invoice.addProduct(new DairyProduct("Maslo", new BigDecimal("100")));
+        // price with tax: 12.30
+        invoice.addProduct(new OtherProduct("Chipsy", new BigDecimal("10")));
+        Assert.assertThat(new BigDecimal("320.30"), Matchers.comparesEqualTo(invoice.getTotal()));
+    }
+
+    @Test
+    public void testInvoiceHasPropoerSubtotalWithQuantityMoreThanOne() {
+        // 2x kubek - price: 10
+        invoice.addProduct(new TaxFreeProduct("Kubek", new BigDecimal("5")), 2);
+        // 3x kozi serek - price: 30
+        invoice.addProduct(new DairyProduct("Kozi Serek", new BigDecimal("10")), 3);
+        // 1000x pinezka - price: 10
+        invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
+        Assert.assertThat(new BigDecimal("50"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+    }
+
+    @Test
+    public void testInvoiceHasPropoerTotalWithQuantityMoreThanOne() {
+        // 2x chleb - price with tax: 10
+        invoice.addProduct(new TaxFreeProduct("Chleb", new BigDecimal("5")), 2);
+        // 3x chedar - price with tax: 32.40
+        invoice.addProduct(new DairyProduct("Chedar", new BigDecimal("10")), 3);
+        // 1000x pinezka - price with tax: 12.30
+        invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
+        Assert.assertThat(new BigDecimal("54.70"), Matchers.comparesEqualTo(invoice.getTotal()));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testInvoiceWithZeroQuantity() {
+        invoice.addProduct(new TaxFreeProduct("Tablet", new BigDecimal("1678")), 0);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testInvoiceWithNegativeQuantity() {
+        invoice.addProduct(new DairyProduct("Zsiadle mleko", new BigDecimal("5.55")), -1);
+    }
+}
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/product/ProductTest.java b/src/test/java/pl/edu/agh/mwo/invoice/product/ProductTest.java
new file mode 100644
index 000000000..9b3c5bd6e
--- /dev/null
+++ b/src/test/java/pl/edu/agh/mwo/invoice/product/ProductTest.java
@@ -0,0 +1,57 @@
+package pl.edu.agh.mwo.invoice.product;
+
+import java.math.BigDecimal;
+
+import org.hamcrest.Matchers;
+import org.junit.Assert;
+import org.junit.Test;
+
+import pl.edu.agh.mwo.invoice.product.Product;
+
+public class ProductTest {
+    @Test
+    public void testProductNameIsCorrect() {
+        Product product = new OtherProduct("buty", new BigDecimal("100.0"));
+        Assert.assertEquals("buty", product.getName());
+    }
+
+    @Test
+    public void testProductPriceAndTaxWithDefaultTax() {
+        Product product = new OtherProduct("Ogorki", new BigDecimal("100.0"));
+        Assert.assertThat(new BigDecimal("100"), Matchers.comparesEqualTo(product.getPrice()));
+        Assert.assertThat(new BigDecimal("0.23"), Matchers.comparesEqualTo(product.getTaxPercent()));
+    }
+
+    @Test
+    public void testProductPriceAndTaxWithDairyProduct() {
+        Product product = new DairyProduct("Szarlotka", new BigDecimal("100.0"));
+        Assert.assertThat(new BigDecimal("100"), Matchers.comparesEqualTo(product.getPrice()));
+        Assert.assertThat(new BigDecimal("0.08"), Matchers.comparesEqualTo(product.getTaxPercent()));
+    }
+
+    @Test
+    public void testPriceWithTax() {
+        Product product = new DairyProduct("Oscypek", new BigDecimal("100.0"));
+        Assert.assertThat(new BigDecimal("108"), Matchers.comparesEqualTo(product.getPriceWithTax()));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testProductWithNullName() {
+        new OtherProduct(null, new BigDecimal("100.0"));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testProductWithEmptyName() {
+        new TaxFreeProduct("", new BigDecimal("100.0"));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testProductWithNullPrice() {
+        new DairyProduct("Banany", null);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testProductWithNegativePrice() {
+        new TaxFreeProduct("Mandarynki", new BigDecimal("-1.00"));
+    }
+}