Add more CFE tests for server

Change-Id: I51b36a988c83e2f20f3e76d01fdb09644c2c2ce2
Reviewed-on: https://dart-review.googlesource.com/68760
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/test/abstract_context.dart

@@ -112,6 +112,33 @@ class _IsTestGroup {
     return source;
   }
 
+  /**
+   * Call a test that we think will fail.
+   *
+   * Ensure that we return any thrown exception correctly (avoiding the
+   * package:test zone error handler).
+   */
+  Future callFailingTest(Future Function() expectedFailingTestFn) {
+    final Completer completer = new Completer();
+
+    try {
+      runZoned(
+        () async => await expectedFailingTestFn(),
+        onError: (error) {
+          completer.completeError(error);
+        },
+      ).then((result) {
+        completer.complete(result);
+      }).catchError((error) {
+        completer.completeError(error);
+      });
+    } catch (error) {
+      completer.completeError(error);
+    }
+
+    return completer.future;
+  }
+
   /**
    * Re-configure the driver. This is necessary, for example, after defining a
    * new package that test code will reference.