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..0fc89c9e9 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 +1,50 @@
 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;
-
-    public void addProduct(Product product) {
-        // TODO: implement
-    }
-
-    public void addProduct(Product product, Integer quantity) {
-        // TODO: implement
-    }
-
-    public BigDecimal getSubtotal() {
-        return null;
-    }
-
-    public BigDecimal getTax() {
-        return null;
-    }
-
-    public BigDecimal getTotal() {
-        return null;
-    }
+	//private Collection<Product> products;
+	private Map<Product, Integer> products = new LinkedHashMap<>();
+
+	public void addProduct(Product product) {
+		products.put(product, 1);
+	}
+
+	public void addProduct(Product product, Integer quantity) {
+		if (quantity <= 0) {
+			throw new IllegalArgumentException("Cannot add product with negative or zero quantity");
+		}
+		products.put(product, quantity);
+	}
+
+	public BigDecimal getSubtotal() {
+		BigDecimal subTotal = BigDecimal.ZERO;
+		for (Product product : this.products.keySet()) {
+			Integer quantity = this.products.get(product);
+			subTotal = subTotal.add(product.getPrice().multiply(new BigDecimal(quantity)));
+		}
+		return subTotal;
+	}
+
+	public BigDecimal getTax() {
+		BigDecimal tax = BigDecimal.ZERO;
+		BigDecimal percent = new BigDecimal("10");
+		for (Product product : this.products.keySet()) {
+			tax = tax.add(product.getTaxPercent()).multiply(percent);
+		}
+		return tax;
+	}
+
+	public BigDecimal getTotal() {
+		BigDecimal total = BigDecimal.ZERO;
+		for (Product product : this.products.keySet()) {
+			Integer quantity = this.products.get(product);
+			total = total.add(product.getPriceWithTax().multiply(new BigDecimal(quantity)));
+		}
+		return total;
+	}
 }
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..673bfb6bf 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
@@ -3,31 +3,39 @@
 import java.math.BigDecimal;
 
 public abstract class Product {
-    private final String name;
-
-    private final BigDecimal price;
-
-    private final BigDecimal taxPercent;
-
-    protected Product(String name, BigDecimal price, BigDecimal tax) {
-        this.name = name;
-        this.price = price;
-        this.taxPercent = tax;
-    }
-
-    public String getName() {
-        return null;
-    }
-
-    public BigDecimal getPrice() {
-        return null;
-    }
-
-    public BigDecimal getTaxPercent() {
-        return null;
-    }
-
-    public BigDecimal getPriceWithTax() {
-        return null;
-    }
-}
+	
+	private final String name;
+
+	private final BigDecimal price;
+
+	private final BigDecimal taxPercent;
+
+	protected Product(String name, BigDecimal price, BigDecimal tax) {
+
+		if (name == null || name.equals("")) {
+			throw new IllegalArgumentException("You cannot create products with null name!");
+		}
+		this.name = name;
+		if (price == null || price.intValue() < 0) {
+			throw new IllegalArgumentException("You cannot create products with null or negative price!");
+		}
+		this.price = price;
+		this.taxPercent = tax;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public BigDecimal getPrice() {
+		return this.price;
+	}
+
+	public BigDecimal getTaxPercent() {
+		return this.taxPercent;
+	}
+
+	public BigDecimal getPriceWithTax() {
+		return this.price.add(this.price.multiply(this.taxPercent));
+	}
+}
\ No newline at end of file
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"));
+    }
+}