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 28f0847a8..f3ae1013e 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -2,29 +2,54 @@
 
 import java.math.BigDecimal;
 import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
 
 import pl.edu.agh.mwo.invoice.product.Product;
 
 public class Invoice {
-	private Collection<Product> products;
+//	private Collection<Product> products
+	private Map<Product, Integer> products =  new HashMap<>();
 
 	public void addProduct(Product product) {
-		// TODO: implement
+		this.addProduct(product, 1);
+//		if (products.containsKey(product)) {
+//			int a = products.get(product);
+//			products.put(product,a+1);
+//		}
+//		products.put(product,1);
 	}
 
 	public void addProduct(Product product, Integer quantity) {
-		// TODO: implement
+		if (products.containsKey(product)) {
+			int a = products.get(product);
+			products.put(product,quantity+1);
+		}
+		products.put(product,quantity);
 	}
 
-	public BigDecimal getSubtotal() {
-		return null;
+	public BigDecimal getNetPrice() {
+		BigDecimal sum = new BigDecimal ("0");
+		for(Product s : this.products.keySet()){
+			Integer amount = this.products.get(s);
+			BigDecimal a = new BigDecimal(amount);
+			BigDecimal price = s.getPrice();
+			sum = sum.add(price.multiply(a));
+		}
+		return sum;
 	}
 
 	public BigDecimal getTax() {
-		return null;
+		return this.getGrossPrice().subtract(this.getNetPrice());
 	}
 
-	public BigDecimal getTotal() {
-		return null;
+	public BigDecimal getGrossPrice() {
+		BigDecimal gross = new BigDecimal("0");
+		for(Product s : this.products.keySet()){
+			BigDecimal a = new BigDecimal(this.products.get(s));
+			BigDecimal tax = s.getPriceWithTax().subtract(s.getPrice());
+			gross = gross.add(tax.multiply(a));
+		}
+		return gross;
 	}
 }
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 b75785935..01c670a73 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 +10,38 @@ 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 can't be null!");
+		}
+		if (price == null)
+		{
+		throw new IllegalArgumentException();
+		}
+		if (price.compareTo(new BigDecimal ("0")) < 0)
+		{
+		throw new IllegalArgumentException();
+		}
 		this.name = name;
 		this.price = price;
 		this.taxPercent = tax;
 	}
 
 	public String getName() {
-		return null;
+		return name;
 	}
 
 	public BigDecimal getPrice() {
-		return null;
+		return price;
 	}
 
 	public BigDecimal getTaxPercent() {
-		return null;
+		return taxPercent;
 	}
 
 	public BigDecimal getPriceWithTax() {
-		return null;
+		BigDecimal a = new BigDecimal ("1");
+		return (price.multiply((taxPercent.add(a))));
+
 	}
 }
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..9010eada3
--- /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.getNetPrice()));
+	}
+
+	@Test
+	public void testEmptyInvoiceHasEmptyTaxAmount() {
+		Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTax()));
+	}
+
+	@Test
+	public void testEmptyInvoiceHasEmptyTotal() {
+		Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getGrossPrice()));
+	}
+
+	@Test
+	public void testInvoiceHasTheSameSubtotalAndTotalIfTaxIsZero() {
+		Product taxFreeProduct = new TaxFreeProduct("Warzywa", new BigDecimal("199.99"));
+		invoice.addProduct(taxFreeProduct);
+		Assert.assertThat(invoice.getGrossPrice(), Matchers.comparesEqualTo(invoice.getNetPrice()));
+	}
+
+	@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.getNetPrice()));
+	}
+
+	@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.getGrossPrice()));
+	}
+
+	@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.getNetPrice()));
+	}
+
+	@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.getGrossPrice()));
+	}
+
+	@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..832ae2c96
--- /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"));
+	}
+}