Put test behind a compat flag

test/app.router.js

@@ -188,19 +188,21 @@ describe('app.router', function(){
       .expect('editing user 10', done);
     })
 
-    it('should populate req.params with named captures', function(done){
-      var app = express();
+    if (supportsRegexp('(?<foo>.*)')) {
+      it('should populate req.params with named captures', function(done){
+        var app = express();
 
-      app.get(/^\/user\/(?<userId>[0-9]+)\/(view|edit)?$/, function(req, res){
-        var id = req.params.userId
-          , op = req.params[0];
-        res.end(op + 'ing user ' + id);
-      });
+        app.get(/^\/user\/(?<userId>[0-9]+)\/(view|edit)?$/, function(req, res){
+          var id = req.params.userId
+            , op = req.params[0];
+          res.end(op + 'ing user ' + id);
+        });
 
-      request(app)
-      .get('/user/10/edit')
-      .expect('editing user 10', done);
-    })
+        request(app)
+        .get('/user/10/edit')
+        .expect('editing user 10', done);
+      })
+    }
 
     it('should ensure regexp matches path prefix', function (done) {
       var app = express()
@@ -1123,3 +1125,12 @@ describe('app.router', function(){
     assert.strictEqual(app.get('/', function () {}), app)
   })
 })
+
+function supportsRegexp(source) {
+  try {
+    new RegExp(source)
+    return true
+  } catch (e) {
+    return false
+  }
+}