remove TestOnlyCopyToVector() from LB metadata API

src/core/client_channel/lb_metadata.cc

@@ -61,7 +61,7 @@ absl::optional<absl::string_view> LbMetadata::Lookup(
 }
 
 std::vector<std::pair<std::string, std::string>>
-LbMetadata::TestOnlyCopyToVector() {
+LbMetadata::TestOnlyCopyToVector() const {
   if (batch_ == nullptr) return {};
   Encoder encoder;
   batch_->Encode(&encoder);

src/core/client_channel/lb_metadata.h

@@ -33,8 +33,7 @@ class LbMetadata : public LoadBalancingPolicy::MetadataInterface {
   absl::optional<absl::string_view> Lookup(absl::string_view key,
                                            std::string* buffer) const override;
 
-  std::vector<std::pair<std::string, std::string>> TestOnlyCopyToVector()
-      override;
+  std::vector<std::pair<std::string, std::string>> TestOnlyCopyToVector() const;
 
  private:
   grpc_metadata_batch* batch_;

src/core/load_balancing/lb_policy.h

@@ -23,7 +23,6 @@
 #include <memory>
 #include <string>
 #include <utility>
-#include <vector>
 
 #include "absl/base/thread_annotations.h"
 #include "absl/container/inlined_vector.h"
@@ -120,10 +119,6 @@ class LoadBalancingPolicy : public InternallyRefCounted<LoadBalancingPolicy> {
 
     virtual absl::optional<absl::string_view> Lookup(
         absl::string_view key, std::string* buffer) const = 0;
-
-    /// Produce a vector of metadata key/value strings for tests.
-    virtual std::vector<std::pair<std::string, std::string>>
-    TestOnlyCopyToVector() = 0;
   };
 
   /// A list of metadata mutations to be returned along with a PickResult.

test/core/load_balancing/lb_policy_test_lib.h

@@ -628,11 +628,6 @@ class LoadBalancingPolicyTest : public ::testing::Test {
       return it->second;
     }
 
-    std::vector<std::pair<std::string, std::string>> TestOnlyCopyToVector()
-        override {
-      return {};  // Not used.
-    }
-
     std::map<std::string, std::string> metadata_;
   };
 

test/core/test_util/BUILD

@@ -333,10 +333,12 @@ grpc_cc_library(
         "//:uri_parser",
         "//src/core:channel_args",
         "//src/core:delegating_helper",
+        "//src/core:down_cast",
         "//src/core:error",
         "//src/core:grpc_backend_metric_data",
         "//src/core:json",
         "//src/core:json_util",
+        "//src/core:lb_metadata",
         "//src/core:lb_policy",
         "//src/core:lb_policy_factory",
         "//src/core:lb_policy_registry",

test/core/test_util/test_lb_policies.cc

@@ -30,9 +30,11 @@
 #include <grpc/grpc.h>
 #include <grpc/support/json.h>
 
+#include "src/core/client_channel/lb_metadata.h"
 #include "src/core/lib/address_utils/parse_address.h"
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/config/core_configuration.h"
+#include "src/core/lib/gprpp/down_cast.h"
 #include "src/core/lib/gprpp/orphanable.h"
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
 #include "src/core/lib/gprpp/status_helper.h"
@@ -129,7 +131,8 @@ class TestPickArgsLb : public ForwardingLoadBalancingPolicy {
       // Report args seen.
       PickArgsSeen args_seen;
       args_seen.path = std::string(args.path);
-      args_seen.metadata = args.initial_metadata->TestOnlyCopyToVector();
+      args_seen.metadata =
+          DownCast<LbMetadata*>(args.initial_metadata)->TestOnlyCopyToVector();
       cb_(args_seen);
       // Do pick.
       return delegate_picker_->Pick(args);
@@ -269,7 +272,8 @@ class InterceptRecvTrailingMetadataLoadBalancingPolicy
       args_seen.status = args.status;
       args_seen.backend_metric_data =
           args.backend_metric_accessor->GetBackendMetricData();
-      args_seen.metadata = args.trailing_metadata->TestOnlyCopyToVector();
+      args_seen.metadata =
+          DownCast<LbMetadata*>(args.trailing_metadata)->TestOnlyCopyToVector();
       cb_(args_seen);
     }