Properly print an error when failing to load a transformer.

sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_from_a_deps_dev_dependency_test.dart

Index: sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_from_a_deps_dev_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/runs_one_third_party_transformer_on_another_test.dart b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_from_a_deps_dev_dependency_test.dart
similarity index 56%
copy from sdk/lib/_internal/pub/test/transformer/runs_one_third_party_transformer_on_another_test.dart
copy to sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_from_a_deps_dev_dependency_test.dart
index 079e3776d7ee12991371df5e360aff39e4500492..300883544fdf3052c2fe61b6d0c6772f4d46bc4d 100644
--- a/sdk/lib/_internal/pub/test/transformer/runs_one_third_party_transformer_on_another_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_from_a_deps_dev_dependency_test.dart
@@ -4,6 +4,9 @@
 
 library pub_tests;
 
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
@@ -11,46 +14,37 @@ import '../serve/utils.dart';
 main() {
   initConfig();
   withBarbackVersions("any", () {
-    integration("runs one third-party transformer on another", () {
-      d.dir("foo", [
-        d.pubspec({
-          "name": "foo",
-          "version": "1.0.0"
-        }),
-        d.dir("lib", [
-          d.file("transformer.dart", dartTransformer('foo')),
-        ])
-      ]).create();
-
+    integration("fails to load a transform from a non-dependency", () {
       d.dir("bar", [
         d.pubspec({
           "name": "bar",
           "version": "1.0.0",
-          "transformers": ["foo/transformer"],
-          "dependencies": {"foo": {"path": "../foo"}}
         }),
         d.dir("lib", [
           d.file("transformer.dart", dartTransformer('bar')),
         ])
       ]).create();
 
+      d.dir("foo", [
+        d.pubspec({
+          "name": "foo",
+          "version": "1.0.0",
+          "dev_dependencies": {"bar": {"path": "../bar"}},
+          "transformers": ["bar"]
+        })
+      ]).create();
+
       d.dir(appPath, [
         d.pubspec({
           "name": "myapp",
-          "transformers": ["bar/transformer"],
-          "dependencies": {'bar': {'path': '../bar'}}
-        }),
-        d.dir("web", [
-          d.file("main.dart", 'const TOKEN = "main.dart";')
-        ])
+          "dependencies": {"foo": {"path": "../foo"}}
+        })
       ]).create();
 
-      createLockFile('myapp', sandbox: ['foo', 'bar'], pkg: ['barback']);
-
-      pubServe();
-      requestShouldSucceed("main.dart",
-          'const TOKEN = "(main.dart, (bar, foo))";');
-      endPubServe();
+      var pub = startPubServe();
+      pub.stderr.expect(contains('Error loading transformer "bar": package '
+          '"bar" is not a dependency.'));
+      pub.shouldExit(exit_codes.DATA);
     });
   });
 }