diff -r 251d0ed461fb -r 58ec6da75f6f task4/solution07/test/org/apidesign/apifest08/test/ContractImposingDelegatingConvertor.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution07/test/org/apidesign/apifest08/test/ContractImposingDelegatingConvertor.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,53 @@
+/*
+ * To change this template, choose Tools | Templates
+ * and open the template in the editor.
+ */
+
+package org.apidesign.apifest08.test;
+
+import java.math.BigDecimal;
+import java.util.Currency;
+import junit.framework.Assert;
+import org.apidesign.apifest08.currency.Convertor;
+import org.apidesign.apifest08.currency.DelegatingConvertor;
+import org.apidesign.apifest08.currency.MonetaryAmount;
+
+/**
+ * A delegating convertor that checks preconditions and postconditions.
+ * Useful for testing.
+ * @author jdvorak
+ */
+public class ContractImposingDelegatingConvertor extends DelegatingConvertor {
+
+    public ContractImposingDelegatingConvertor( final Convertor underlyingConvertor ) {
+        super( underlyingConvertor );
+    }
+
+    @Override
+    public ConversionResult convert( final ConversionRequest req ) {
+        Assert.assertNotNull( "The request", req );
+        final ConversionResult result = super.convert( req );
+        Assert.assertNotNull( "Result of the convert() call", result );
+        final MonetaryAmount netAmount = result.getNetAmount();
+        if ( netAmount != null ) {
+            Assert.assertEquals( "Converted to a different currency than specified in the request", req.getTgtCurrency(), netAmount.getCurrency() );
+        }
+        return result;
+    }
+
+    /**
+     * Do some tests on our own.
+     * @return this
+     */
+    public Convertor test() {
+        try {
+            final Currency aCurrency = Currency.getInstance( "EUR" );
+            new ConversionRequest( new MonetaryAmount( BigDecimal.ONE, aCurrency ), aCurrency );
+            Assert.fail( "Should have thrown an IllegalArgumentException" );
+        } catch ( final IllegalArgumentException e ) {
+            Assert.assertEquals( "Cannot request conversion from EUR to EUR", e.getMessage() );
+        }
+        return this;
+    }
+
+}