Run pub tests against older versions of barback.

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

Index: sdk/lib/_internal/pub/test/transformer/runs_a_transformer_group_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/runs_a_transformer_group_test.dart b/sdk/lib/_internal/pub/test/transformer/runs_a_transformer_group_test.dart
index b0a17ec94c25d8bda1ffaad3c16f5714b0a5ee93..fa696bc7b57ec347dbd9005085f697c4be975702 100644
--- a/sdk/lib/_internal/pub/test/transformer/runs_a_transformer_group_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/runs_a_transformer_group_test.dart
@@ -22,25 +22,27 @@ class RewriteGroup implements TransformerGroup {
 
 main() {
   initConfig();
-  integration("runs a transformer group", () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "transformers": ["myapp/src/group"]
-      }),
-      d.dir("lib", [d.dir("src", [
-        d.file("transformer.dart", REWRITE_TRANSFORMER),
-        d.file("group.dart", GROUP)
-      ])]),
-      d.dir("web", [
-        d.file("foo.txt", "foo")
-      ])
-    ]).create();
-
-    createLockFile('myapp', pkg: ['barback']);
-
-    pubServe();
-    requestShouldSucceed("foo.out", "foo.out");
-    endPubServe();
+  withBarbackVersions("any", () {
+    integration("runs a transformer group", () {
+      d.dir(appPath, [
+        d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/group"]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", REWRITE_TRANSFORMER),
+          d.file("group.dart", GROUP)
+        ])]),
+        d.dir("web", [
+          d.file("foo.txt", "foo")
+        ])
+      ]).create();
+
+      createLockFile('myapp', pkg: ['barback']);
+
+      pubServe();
+      requestShouldSucceed("foo.out", "foo.out");
+      endPubServe();
+    });
   });
 }