diff -r c1d43bc1e9c0 -r 58ec6da75f6f task4/solution07/test/org/apidesign/apifest08/test/Task3Test.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution07/test/org/apidesign/apifest08/test/Task3Test.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,135 @@
+package org.apidesign.apifest08.test;
+
+import java.math.BigDecimal;
+import java.util.Currency;
+import junit.framework.TestCase;
+import org.apidesign.apifest08.currency.Convertor;
+import org.apidesign.apifest08.currency.MonetaryAmount;
+import org.apidesign.apifest08.currency.anothervendor.ZigZaggingBidirectionalConvertor;
+
+/** 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 {
+    }
+
+    protected static final Currency CZK = Currency.getInstance( "CZK" );
+    protected static final Currency SKK = Currency.getInstance( "SKK" );
+    protected static final Currency USD = Currency.getInstance( "USD" );
+
+    // 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.
+        final MonetaryAmount oneUSD = new MonetaryAmount( 1, USD );
+        final BigDecimal startAmount = new BigDecimal( 16 );
+        final BigDecimal endAmount = new BigDecimal( 15 );
+        final BigDecimal stepAmount = BigDecimal.ONE.movePointLeft( 2 ).negate();
+        return new ContractImposingDelegatingConvertor( new ZigZaggingBidirectionalConvertor( oneUSD, CZK, startAmount, endAmount, stepAmount ) );
+    }
+
+    public void testFewQueriesForOnlineConvertor() {
+        Convertor c = createOnlineCZKUSDConvertor();
+        doFewQueriesForOnlineConvertor(c);
+    }
+
+    static void doFewQueriesForOnlineConvertor( final Convertor c ) {
+        // convert $5 to CZK using c:
+        final Convertor.ConversionResult r1 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( 5, USD ), CZK ) );
+        final MonetaryAmount a1 = r1.getNetAmount();
+        //assertEquals("Result is 80 CZK");
+        assertNotNull( a1 );
+        assertEquals( 80.0, a1.getAmount().doubleValue() );
+        assertEquals( CZK, a1.getCurrency() );
+
+        // convert $8 to CZK using c:
+        final Convertor.ConversionResult r2 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( 8, USD ), CZK ) );
+        final MonetaryAmount a2 = r2.getNetAmount();
+        //assertEquals("Result is 127.92 CZK");
+        assertNotNull( a2 );
+        assertEquals( 12792.0, a2.getAmount().movePointRight( 2 ).doubleValue() );
+        assertEquals( CZK, a2.getCurrency() );
+
+        // convert $1 to CZK using c:
+        final Convertor.ConversionResult r3 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( 1, USD ), CZK ) );
+        final MonetaryAmount a3 = r3.getNetAmount();
+        //assertEquals("Result is 15.98 CZK");
+        assertNotNull( a3 );
+        assertEquals( 1598.0, a3.getAmount().movePointRight( 2 ).doubleValue() );
+        assertEquals( CZK, a3.getCurrency() );
+
+        // convert 15.97CZK to USD using c:
+        final BigDecimal s4 = new BigDecimal( 1597 ).movePointLeft( 2 );
+        final Convertor.ConversionResult r4 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( s4, CZK ), USD ) );
+        final MonetaryAmount a4 = r4.getNetAmount();
+        //assertEquals("Result is 1$");
+        assertNotNull( a4 );
+        assertEquals( 1.0, a4.getAmount().doubleValue() );
+        assertEquals( USD, a4.getCurrency() );
+    }
+
+    /** Join the convertors and show they behave sane.
+     */
+    public void testOnlineConvertorComposition() throws Exception {
+        final Convertor c = Task2Test.merge(
+            createOnlineCZKUSDConvertor(),
+            Task1Test.createSKKtoCZK()
+        );
+
+        // convert 16CZK using c:
+        final Convertor.ConversionResult r4 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( 16, CZK ), SKK ) );
+        final MonetaryAmount a4 = r4.getNetAmount();
+        // assertEquals("Result is 20 SKK");
+        assertNotNull( a4 );
+        assertEquals( 20.0, a4.getAmount().doubleValue() );
+        assertEquals( SKK, a4.getCurrency() );
+
+        // convert 500SKK to CZK using c:
+        final Convertor.ConversionResult r5 = c.convert( new Convertor.ConversionRequest( new MonetaryAmount( 500, SKK ), CZK ) );
+        final MonetaryAmount a5 = r5.getNetAmount();
+        // assertEquals("Result is 400 CZK");
+        assertNotNull( a5 );
+        assertEquals( 400.0, a5.getAmount().doubleValue() );
+        assertEquals( CZK, a5.getCurrency() );
+
+        doFewQueriesForOnlineConvertor(c);
+    }
+}