Install barback from a hosted source in all tests.

test/transformer/prints_a_transform_interface_error_test.dart

Index: test/transformer/prints_a_transform_interface_error_test.dart
diff --git a/test/transformer/prints_a_transform_interface_error_test.dart b/test/transformer/prints_a_transform_interface_error_test.dart
index 9cd32670ce9f84bf230540e72d8865e83d9d5c00..1e3dfee1d5f53605feb0ff742d51269579de283e 100644
--- a/test/transformer/prints_a_transform_interface_error_test.dart
+++ b/test/transformer/prints_a_transform_interface_error_test.dart
@@ -22,10 +22,13 @@ class RewriteTransformer extends Transformer {
 
 main() {
   integration("prints a transform interface error", () {
+    serveBarback();
+
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
-        "transformers": ["myapp/src/transformer"]
+        "transformers": ["myapp/src/transformer"],
+        "dependencies": {"barback": "any"}
       }),
       d.dir("lib", [d.dir("src", [
         d.file("transformer.dart", transformer)
@@ -35,8 +38,7 @@ main() {
       ])
     ]).create();
 
-    createLockFile('myapp', pkg: ['barback']);
-
+    pubGet();
     var server = pubServe();
     server.stderr.expect(emitsLines(
         "Build error:\n"