Run pub tests against older versions of barback.

sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart

Index: sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart b/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
index 1d8a1cf6b35c049e043bc953948e1e0b814ae414..3f7f48ecdb41fa9383678f9f5c7af09e7ad760b7 100644
--- a/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
@@ -35,24 +35,26 @@ class ConfigTransformer extends Transformer {
 
 main() {
   initConfig();
-  integration("configuration defaults to an empty map", () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "transformers": ["myapp/src/transformer"]
-      }),
-      d.dir("lib", [d.dir("src", [
-        d.file("transformer.dart", transformer)
-      ])]),
-      d.dir("web", [
-        d.file("foo.txt", "foo")
-      ])
-    ]).create();
-
-    createLockFile('myapp', pkg: ['barback']);
-
-    var server = pubServe();
-    requestShouldSucceed("foo.json", JSON.encode({}));
-    endPubServe();
+  withBarbackVersions("any", () {
+    integration("configuration defaults to an empty map", () {
+      d.dir(appPath, [
+        d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/transformer"]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", transformer)
+        ])]),
+        d.dir("web", [
+          d.file("foo.txt", "foo")
+        ])
+      ]).create();
+
+      createLockFile('myapp', pkg: ['barback']);
+
+      var server = pubServe();
+      requestShouldSucceed("foo.json", JSON.encode({}));
+      endPubServe();
+    });
   });
 }