added link for writing test cases

tests/readme-tests-module.html

@@ -119,8 +119,10 @@ To write a new test, evolve an existing example.  See the dtd and/or
 the javadoc for the testing harness implementation in the 
 <code>testing</code> module for more details.
 
-<p>To write a test case for a bug, see XXX todo.
-   
+<p>To write a test case for a bug, see 
+  <a href="readme-writing-compiler-tests.html">
+           readme-writing-compiler-tests.html</a>.
+           
 <h3><a name="#product"></a>Product</h3>
 Product tests target a built distribution or do compiler (argument) 
 testing not supported by the harness.