diff -r c1d43bc1e9c0 -r 58ec6da75f6f task4/solution06/test/org/apidesign/apifest08/test/Task3Test.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution06/test/org/apidesign/apifest08/test/Task3Test.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,111 @@
+package org.apidesign.apifest08.test;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+import junit.framework.TestCase;
+import org.apidesign.apifest08.currency.Convertor;
+import static org.apidesign.apifest08.test.Currencies.*;
+
+/** 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 {
+    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() {
+    	Convertor.RateProvider rateProvider = new Convertor.RateProvider() {
+    		private BigDecimal seed = new BigDecimal("16.01").setScale(2);
+    		
+			@Override
+			public BigDecimal getRate() {
+				if(seed.equals(new BigDecimal("15").setScale(2))) {
+					seed = seed.add(new BigDecimal("0.01")).setScale(2);
+				} else {
+					seed = seed.subtract(new BigDecimal("0.01")).setScale(2);
+				}	
+				return seed;
+			}
+    		
+    	};
+    	
+        // 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.
+        return new Convertor(rateProvider, USD, CZK);
+    }
+
+    public void testFewQueriesForOnlineConvertor() {
+        Convertor c = createOnlineCZKUSDConvertor();
+        doFewQueriesForOnlineConvertor(c);
+    }
+
+    static void doFewQueriesForOnlineConvertor(Convertor c) {
+        // convert $5 to CZK using c:
+        assertEquals("Result is 80 CZK",80 ,c.convert(new BigDecimal(5), USD, CZK).getValue().intValue());
+
+        // convert $8 to CZK using c:
+        assertEquals("Result is 127.92 CZK", 127.92d , c.convert(new BigDecimal(8), USD, CZK).getValue().doubleValue());
+
+        // convert $1 to CZK using c:
+        assertEquals("Result is 15.98 CZK", 15.98d,  c.convert(new BigDecimal(1), USD, CZK).getValue().doubleValue());
+
+        // convert 15.97CZK to USD using c:
+        assertEquals("Result is 1$", 1, c.convert(new BigDecimal("15.97").setScale(2), CZK, USD).getValue().intValue());
+    }
+
+    /** 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 SKK", 20, c.convert(new BigDecimal(16), CZK, SKK).getValue().intValue());
+
+        // convert 500SKK to CZK using c:
+        assertEquals("Result is 400 CZK", 400, c.convert(new BigDecimal(500), SKK, CZK).getValue().intValue());
+
+        doFewQueriesForOnlineConvertor(c);
+    }
+}