Ensure exceptions from methodBlock() don't result in unrooted tests

The introduction of the runLeaf() method in BlockJUnit4ClassRunner in
JUnit 4.9 introduced a regression with regard to exception handling.

Specifically, the invocation of methodBlock() is no longer executed
within a try-catch block as was the case in previous versions of JUnit.

Custom modifications to methodBlock() or the methods it invokes may in
fact throw exceptions. In such cases, exceptions thrown from
methodBlock() cause the current test execution to abort immediately. As
a result, the failing test method is unrooted in test reports, and
subsequent test methods are never invoked. Furthermore, RunListeners
registered with JUnit are not notified.

This commit addresses this issue by wrapping the invocation of
methodBlock() within a try-catch block. If an exception is not thrown,
the resulting Statement is passed to runLeaf(). If an exception is
thrown, it is wrapped in a Fail statement which is passed to runLeaf().

Issue: #1066

src/main/java/org/junit/runners/BlockJUnit4ClassRunner.java

@@ -55,7 +55,9 @@
  * @since 4.5
  */
 public class BlockJUnit4ClassRunner extends ParentRunner<FrameworkMethod> {
+
     private final ConcurrentHashMap<FrameworkMethod, Description> methodDescriptions = new ConcurrentHashMap<FrameworkMethod, Description>();
+
     /**
      * Creates a BlockJUnit4ClassRunner to run {@code testClass}
      *
@@ -75,10 +77,17 @@ protected void runChild(final FrameworkMethod method, RunNotifier notifier) {
         if (isIgnored(method)) {
             notifier.fireTestIgnored(description);
         } else {
-            runLeaf(methodBlock(method), description, notifier);
+            Statement statement;
+            try {
+                statement = methodBlock(method);
+            }
+            catch (Throwable ex) {
+                statement = new Fail(ex);
+            }
+            runLeaf(statement, description, notifier);
         }
     }
-    
+
     /**
      * Evaluates whether {@link FrameworkMethod}s are ignored based on the
      * {@link Ignore} annotation.
@@ -390,10 +399,10 @@ private List<org.junit.rules.MethodRule> getMethodRules(Object target) {
     protected List<MethodRule> rules(Object target) {
         List<MethodRule> rules = getTestClass().getAnnotatedMethodValues(target, 
                 Rule.class, MethodRule.class);
-        
+
         rules.addAll(getTestClass().getAnnotatedFieldValues(target,
                 Rule.class, MethodRule.class));
-        
+
         return rules;
     }