diff -r c1d43bc1e9c0 -r 58ec6da75f6f task4/solution13/test/org/apidesign/apifest08/test/Task3Test.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution13/test/org/apidesign/apifest08/test/Task3Test.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,122 @@
+package org.apidesign.apifest08.test;
+
+import java.math.BigDecimal;
+import junit.framework.TestCase;
+import org.apidesign.apifest08.currency.Convertor;
+import org.apidesign.apifest08.currency.ConvertorCurrency;
+import org.apidesign.apifest08.currency.ExchangeRateProvider;
+import org.apidesign.apifest08.currency.IExchangeRateEngine;
+
+/** The exchange rates are not always the same. They are changing. Day by day,
+ * hour by hour, minute by minute. For every bank it is important to always
+ * have the actual exchange rate available in the system. That is why let's
+ * create a pluggable convertor that will always have up to date value of its
+ * exchange rate.
+ * <p>
+ * The quest for today is to allow 3rd party developer to write a convertor
+ * that adjusts its exchange rate everytime it is queried. This convertor is
+ * written by independent vendor, the vendor knows only your Convertor API,
+ * he does not know how the whole system looks and how the convertor is supposed
+ * to be used.
+ */
+public class Task3Test extends TestCase {
+    
+    private static ConvertorCurrency currencyCZK = ConvertorCurrency.getInstance("CZK");
+    private static ConvertorCurrency currencySKK = ConvertorCurrency.getInstance("SKK");
+    private static ConvertorCurrency currencyUSD = ConvertorCurrency.getInstance("USD");
+    
+    public Task3Test(String testName) {
+        super(testName);
+    }
+
+    @Override
+    protected void setUp() throws Exception {
+    }
+
+    @Override
+    protected void tearDown() throws Exception {
+    }
+
+    // Backward compatibly enhance your existing API to support following
+    // usecases:
+    //
+
+
+    /** Without knowing anything about the surrounding system, write an
+     * implementation of convertor that will return different rates everytime
+     * it is queried. Convert USD to CZK and vice versa. Start with the rate of
+     * 1USD = 16CZK and adjust it in favor of CZK by 0.01 CZK with every query.
+     * As soon as you reach 1USD = 15CZK adjust it by 0.01 CZK in favor of USD
+     * until you reach 1USD = 16CZK
+     *
+     * @return new instance of "online" USD and CZK convertor starting with rate 1USD = 16CZK
+     */
+    public static Convertor createOnlineCZKUSDConvertor() {
+        // initial rate: 1USD = 16CZK
+        // 2nd query 1USD = 15.99CZK
+        // 3rd query 1USD = 15.98CZK
+        // until 1USD = 15.00CZK
+        // then 1USD = 15.01CZK
+        // then 1USD = 15.02CZK
+        // and so on and on up to 1USD = 16CZK
+        // and then another round to 15, etc.
+        IExchangeRateEngine engine = BouncingExchangeRateEngine.create(
+                currencyUSD,  new BigDecimal(1),
+                currencyCZK, 
+                new BigDecimal(16),new BigDecimal(15),
+                new BigDecimal("-0.01"));
+        ExchangeRateProvider exRateProvider = ExchangeRateProvider.createExchangeRateProvider(engine);
+        Convertor convertor = Convertor.createConvertor(exRateProvider);
+        return convertor;
+    }
+
+    public void testFewQueriesForOnlineConvertor() {
+        Convertor c = createOnlineCZKUSDConvertor();
+        doFewQueriesForOnlineConvertor(c);
+    }
+
+    static void doFewQueriesForOnlineConvertor(Convertor c) {
+        // convert $5 to CZK using c:
+        assertEquals("Result is 80 CZK", new BigDecimal("80.00"), c.convertWithReversibleRates(currencyUSD, currencyCZK, new BigDecimal(5)).getConverted());
+
+        // convert $8 to CZK using c:
+        assertEquals("Result is 127.92 CZK", new BigDecimal("127.92"), c.convertWithReversibleRates(currencyUSD, currencyCZK, new BigDecimal(8)).getConverted());
+
+        // convert $1 to CZK using c:
+        assertEquals("Result is 15.98 CZK", new BigDecimal("15.98"), c.convertWithReversibleRates(currencyUSD, currencyCZK, new BigDecimal(1)).getConverted());
+
+        // convert 15.97CZK to USD using c:
+        assertEquals("Result is 15.98 CZK", new BigDecimal("1.00"), c.convertWithReversibleRates(currencyCZK, currencyUSD , new BigDecimal("15.97")).getConverted());
+    }
+
+    /** Join the convertors and show they behave sane.
+     */
+    public void testOnlineConvertorComposition() throws Exception {
+        Convertor c = Task2Test.merge(
+            createOnlineCZKUSDConvertor(),
+            Task1Test.createSKKtoCZK()
+        );
+
+        // convert 16CZK to SKK using c:
+        assertEquals("Result is 20 CZK", new BigDecimal("20.00"), c.convertWithReversibleRates(currencyCZK, currencySKK , new BigDecimal("16")).getConverted());
+
+        // convert 500SKK to CZK using c:
+        assertEquals("Result is 400 CZK", new BigDecimal("400.00"), c.convertWithReversibleRates(currencySKK, currencyCZK , new BigDecimal("500")).getConverted());
+
+        doFewQueriesForOnlineConvertor(c);
+    }
+    
+//    public void testBouncing() {
+//        Convertor c=createOnlineCZKUSDConvertor();
+//        
+//        IExchangeRateEngine engine = BouncingExchangeRateEngine.create(
+//                currencyUSD,  new BigDecimal(1),
+//                currencyCZK, 
+//                new BigDecimal("16.00"),new BigDecimal("15.00"),
+//                new BigDecimal("-0.01"));        
+//        
+//        for (int i=0;i<300;i++) {
+//            System.out.println(engine.getExchangeRate(currencyUSD, currencyCZK).getToValue());
+//        }
+//    }
+}