Run pub tests against older versions of barback.

sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart

Index: sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart b/sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart
index b5bf7141556a243b92c9b46553e63e83348ba594..81e41635cf7b637af26b536dd1c0d90a2acde6b3 100644
--- a/sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/exclusion/exclude_asset_string_test.dart
@@ -10,36 +10,38 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("allows a single string as the asset to exclude", () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "transformers": [
-          {
-            "myapp/src/transformer": {
-              "\$exclude": "web/foo.txt"
+  withBarbackVersions("any", () {
+    integration("allows a single string as the asset to exclude", () {
+      d.dir(appPath, [
+        d.pubspec({
+          "name": "myapp",
+          "transformers": [
+            {
+              "myapp/src/transformer": {
+                "\$exclude": "web/foo.txt"
+              }
             }
-          }
-        ]
-      }),
-      d.dir("lib", [d.dir("src", [
-        d.file("transformer.dart", REWRITE_TRANSFORMER)
-      ])]),
-      d.dir("web", [
-        d.file("foo.txt", "foo"),
-        d.file("bar.txt", "bar"),
-        d.dir("sub", [
+          ]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", REWRITE_TRANSFORMER)
+        ])]),
+        d.dir("web", [
           d.file("foo.txt", "foo"),
+          d.file("bar.txt", "bar"),
+          d.dir("sub", [
+            d.file("foo.txt", "foo"),
+          ])
         ])
-      ])
-    ]).create();
+      ]).create();
 
-    createLockFile('myapp', pkg: ['barback']);
+      createLockFile('myapp', pkg: ['barback']);
 
-    pubServe();
-    requestShould404("foo.out");
-    requestShouldSucceed("sub/foo.out", "foo.out");
-    requestShouldSucceed("bar.out", "bar.out");
-    endPubServe();
+      pubServe();
+      requestShould404("foo.out");
+      requestShouldSucceed("sub/foo.out", "foo.out");
+      requestShouldSucceed("bar.out", "bar.out");
+      endPubServe();
+    });
   });
 }