diff -r c1d43bc1e9c0 -r 58ec6da75f6f task4/solution12/test/org/apidesign/apifest08/test/Task3Test.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution12/test/org/apidesign/apifest08/test/Task3Test.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,145 @@
+package org.apidesign.apifest08.test;
+
+import java.util.Currency;
+
+import junit.framework.TestCase;
+import org.apidesign.apifest08.currency.Convertor;
+import org.apidesign.apifest08.currency.exceptions.UnknownConvertorException;
+
+/** 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 double actualRate;
+    private static boolean increasing;
+    
+    private static final double EXCHANGE_RATE_MAX = 16.0;
+    private static final double EXCHANGE_RATE_MIN = 15.0;
+  
+    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() {
+      actualRate = 16.01;
+      increasing = false;
+      
+      // sets actual exchange rates
+      setRates();
+      
+      // create new instance
+      Convertor convertor = null;
+      try {
+        convertor = Convertor.getConvertorInstance(Currency.getInstance("USD"), Currency.getInstance("CZK"));
+      } catch (UnknownConvertorException e) {
+        e.printStackTrace();
+      }
+
+      return convertor;
+    }
+
+    public void testFewQueriesForOnlineConvertor() throws Exception {
+        Convertor c = createOnlineCZKUSDConvertor();
+        doFewQueriesForOnlineConvertor(c);
+    }
+
+    static void doFewQueriesForOnlineConvertor(Convertor c) throws Exception {
+        // convert $5 to CZK using c:
+        double result = c.convert(5d, Currency.getInstance("USD"), Currency.getInstance("CZK"));
+        double expectedResult = actualRate * 5;
+        assertEquals("Result is not " + expectedResult + " CZK", expectedResult, result);
+
+        // change exchange rates
+        setRates();
+        
+        // convert $8 to CZK using c:
+        result = c.convert(8d, Currency.getInstance("USD"), Currency.getInstance("CZK"));
+        expectedResult = actualRate * 8;
+        assertEquals("Result is not " + expectedResult + " CZK", expectedResult, result);
+        
+        // change exchange rates
+        setRates();
+
+        // convert $1 to CZK using c:
+        result = c.convert(1d, Currency.getInstance("USD"), Currency.getInstance("CZK"));
+        expectedResult = actualRate * 1;
+        assertEquals("Result is not " + expectedResult + " CZK", expectedResult, result);
+        
+        // change exchange rates
+        setRates();
+
+        // convert 15.97CZK to USD using c:
+        result = c.convert(15.97d, Currency.getInstance("CZK"), Currency.getInstance("USD"));
+        expectedResult = 15.97 / actualRate ;
+        assertEquals("Result is not " + expectedResult + " USD", expectedResult, result);
+    }
+
+    /** 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:
+        double result = c.convert(16d, Currency.getInstance("CZK"), Currency.getInstance("SKK"));
+        assertEquals("Result is not 20 SKK", 20d, result);
+
+        // convert 500SKK to CZK using c:
+        result = c.convert(500d, Currency.getInstance("SKK"), Currency.getInstance("CZK"));
+        assertEquals("Result is not 400 CZK", 400d, result);
+
+        doFewQueriesForOnlineConvertor(c);
+    }
+    
+    private static void setRates() {
+      // logic for change of actual exchange rate
+      if(increasing) {
+        actualRate += 0.01;
+        if(actualRate == EXCHANGE_RATE_MAX){
+          increasing = false;
+        }
+      } else {
+        actualRate -= 0.01;
+        if(actualRate == EXCHANGE_RATE_MIN){
+          increasing = true;
+        }
+      }
+      
+      // set exchange rates
+      Convertor.setConvertorRates(Currency.getInstance("USD"), Currency.getInstance("CZK"), actualRate, 1d);
+    }
+}