Always ignore non-public transformers.

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

Index: sdk/lib/_internal/pub/test/transformer/ignores_a_transformer_on_test_files_in_a_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/ignores_a_transformer_on_test_files_in_a_dependency_test.dart b/sdk/lib/_internal/pub/test/transformer/ignores_a_transformer_on_test_files_in_a_dependency_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c62c00a15cfcb32ae6d27130c0a0421d96e22cf8
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/transformer/ignores_a_transformer_on_test_files_in_a_dependency_test.dart
@@ -0,0 +1,57 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS d.file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+
+main() {
+  initConfig();
+  // Regression test for issue 23480
+  integration("ignores a transformer on test files in a dependency", () {
+    servePackages((builder) {
+      builder.serveRepoPackage('barback');
+
+      builder.serve("bar", "1.2.3", contents: [
+        d.dir("lib", [
+          // Make this invalid so that if it does get loaded, pub will
+          // definitely throw an error.
+          d.file("bar.dart", "{invalid Dart code)")
+        ])
+      ]);
+
+      builder.serve("foo", "1.2.3",
+        pubspec: {
+        "name": "foo",
+        "version": "1.0.0",
+        "dev_dependencies": {
+          "bar": "any"
+        },
+        "transformers": [{
+          "bar": {"\$include": "test/**"}
+        }]
+      }, contents: [
+        d.dir("test", [
+          d.file("my_test.dart", "void main() {}")
+        ])
+      ]);
+    });
+
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "dependencies": {"foo": "any"}
+      }),
+      d.dir("web", [
+        d.file("foo.txt", "foo")
+      ])
+    ]).create();
+
+    pubGet();
+
+    pubServe();
+    requestShouldSucceed("foo.txt", "foo");
+    endPubServe();
+  });
+}