[book][testing] Making new note about kernel dir shorter

book/testing.rst

@@ -124,31 +124,18 @@ simple functional test for ``DemoController`` that reads as follows::
 
 .. tip::
 
-    While unit tests are built to test each class separately, functional tests
-    need to run the application. For a symfony application to run, it must be
-    bootstrapped correctly, but this is quite simple:
-
-    The phpunit.xml file needs to load app/bootstrap.php.cache which will do the boostrap.
-    Then your test has to load the kernel. When using the ``WebTestCase``, all you need to
-    do is make sure it can locate the kernel php file and the test will instantiate the kernel
-    with the ``test`` environment. If your phpunit.xml file is located in the same directory
-    as your AppKernel.php, this will work automatically. However, if you want to run tests
-    for a bundle or use a non-standard directory structure, you need to specify the location
-    of the kernel directory by defining the php environment variable ``KERNEL_DIR`` to point
-    to the directory containing the kernel.
-
-    The relevant parts of phpunit.xml.dist look like this::
+    To run your functional tests, the ``WebTestCase`` class bootstraps the
+    kernel of your application. In most cases, this happens automatically.
+    However, if your kernel is in a non-standard directory, you'll need
+    to modify your ``phpunit.xml.dist`` file to set the ``KERNEL_DIR`` environment
+    variable to the directory of your kernel::
 
         <phpunit
-            ...
-            bootstrap = "bootstrap.php.cache" >
-            ...
-            <!-- if the kernel is not automatically found, enable and set to kernel path
+            <!-- ... -->
             <php>
                 <server name="KERNEL_DIR" value="/path/to/your/app/" />
             </php>
-            -->
-            ...
+            <!-- ... -->
         </phpunit>