Run pub tests against older versions of barback.

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

Index: sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
index 5e68175ed0dc14d098b9c8a8a07e3ef9cbd9d80a..fb047318c2d6a3710a6d0f45f6d9d7055d2dc1d5 100644
--- a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
@@ -15,20 +15,23 @@ main() {
 
   // An import error will cause the isolate API to fail synchronously while
   // loading the transformer.
-  integration("fails to load a transform with an import error", () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "transformers": ["myapp/src/transformer"]
-      }),
-      d.dir("lib", [d.dir("src", [
-        d.file("transformer.dart", "import 'does/not/exist.dart';")
-      ])])
-    ]).create();
+  withBarbackVersions("any", () {
+    integration("fails to load a transform with an import error", () {
+      d.dir(appPath, [
+        d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/transformer"]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", "import 'does/not/exist.dart';")
+        ])])
+      ]).create();
 
-    createLockFile('myapp', pkg: ['barback']);
-    var pub = startPubServe();
-    pub.stderr.expect(endsWith("error: line 1 pos 1: library handler failed"));
-    pub.shouldExit(1);
+      createLockFile('myapp', pkg: ['barback']);
+      var pub = startPubServe();
+      pub.stderr.expect(
+          endsWith("error: line 1 pos 1: library handler failed"));
+      pub.shouldExit(1);
+    });
   });
 }