Add pretty-printing to unittest and more thoroughly print values.

pkg/unittest/lib/src/operator_matchers.dart

Index: pkg/unittest/lib/src/operator_matchers.dart
diff --git a/pkg/unittest/lib/src/operator_matchers.dart b/pkg/unittest/lib/src/operator_matchers.dart
index d5142bea1a8e3e5aff251b9ea4b83c8e6b481d9f..26e36fc56c35d3e24c9792e4215729ec638354ae 100644
--- a/pkg/unittest/lib/src/operator_matchers.dart
+++ b/pkg/unittest/lib/src/operator_matchers.dart
@@ -94,9 +94,9 @@ class _AllOf extends BaseMatcher {
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     var matcher = matchState.state['matcher'];
-    mismatchDescription.addDescriptionOf(matcher).add(' ');
-        matcher.describeMismatch(item, mismatchDescription,
-            matchState.state['state'], verbose);
+    matcher.describeMismatch(item, mismatchDescription,
+        matchState.state['state'], verbose);
+    mismatchDescription.add(' (').addDescriptionOf(matcher).add(')');
     return mismatchDescription;
   }