Fix Dart 2 runtime failures in tests (#28)

diff --git a/.gitignore b/.gitignore
index 7dbf035..bbe1007 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 # Don’t commit the following directories created by pub.
 .buildlog
 .pub/
+.dart_tool/
 build/
 packages
 .packages
diff --git a/test/authorization_code_grant_test.dart b/test/authorization_code_grant_test.dart
index 9cb1e73..137755c 100644
--- a/test/authorization_code_grant_test.dart
+++ b/test/authorization_code_grant_test.dart
@@ -14,8 +14,8 @@
 final redirectUrl = Uri.parse('http://example.com/redirect');
 
 void main() {
-  var client;
-  var grant;
+  ExpectClient client;
+  oauth2.AuthorizationCodeGrant grant;
   setUp(() {
     client = new ExpectClient();
     grant = new oauth2.AuthorizationCodeGrant(