test: Add dependency injection for remote function thrift client

velox/functions/remote/client/Remote.cpp

@@ -33,12 +33,12 @@ class RemoteThriftFunction : public RemoteVectorFunction {
       const RemoteThriftVectorFunctionMetadata& metadata)
       : RemoteVectorFunction(functionName, inputArgs, metadata),
         location_(metadata.location),
-        thriftClient_(getThriftClient(location_, &eventBase_)) {}
+        client_(createClient(metadata)) {}
 
   std::unique_ptr<remote::RemoteFunctionResponse> invokeRemoteFunction(
       const remote::RemoteFunctionRequest& request) const override {
     auto remoteResponse = std::make_unique<remote::RemoteFunctionResponse>();
-    thriftClient_->sync_invokeFunction(*remoteResponse, request);
+    client_->invokeFunction(*remoteResponse, request);
     return remoteResponse;
   }
 
@@ -47,10 +47,18 @@ class RemoteThriftFunction : public RemoteVectorFunction {
   }
 
  private:
+  std::unique_ptr<IRemoteFunctionClient> createClient(
+      const RemoteThriftVectorFunctionMetadata& metadata) {
+    if (metadata.clientFactory) {
+      return metadata.clientFactory(metadata.location, &eventBase_);
+    }
+    return getDefaultRemoteFunctionClient(metadata.location, &eventBase_);
+  }
+
   folly::SocketAddress location_;
   folly::EventBase eventBase_;
 
-  std::unique_ptr<RemoteFunctionClient> thriftClient_;
+  std::unique_ptr<IRemoteFunctionClient> client_;
 };
 
 std::shared_ptr<exec::VectorFunction> createRemoteFunction(

velox/functions/remote/client/Remote.h

@@ -18,6 +18,7 @@
 
 #include <folly/SocketAddress.h>
 #include "velox/functions/remote/client/RemoteVectorFunction.h"
+#include "velox/functions/remote/client/ThriftClient.h"
 
 namespace facebook::velox::functions {
 
@@ -27,6 +28,11 @@ struct RemoteThriftVectorFunctionMetadata
   /// Note that this can hold a network location (ip/port pair) or a unix domain
   /// socket path (see SocketAddress::makeFromPath()).
   folly::SocketAddress location;
+
+  /// Optional factory for creating remote function clients. If not set, the
+  /// default thrift client factory is used. This enables dependency injection
+  /// for testing with mock clients.
+  RemoteFunctionClientFactory clientFactory;
 };
 
 /// Registers a new remote function. It will use the meatadata defined in

velox/functions/remote/client/ThriftClient.h

@@ -24,8 +24,51 @@ namespace facebook::velox::functions {
 using RemoteFunctionClient =
     apache::thrift::Client<remote::RemoteFunctionService>;
 
+/// Abstract interface for the remote function client, enabling dependency
+/// injection and mocking in tests.
+class IRemoteFunctionClient {
+ public:
+  virtual ~IRemoteFunctionClient() = default;
+
+  /// Invokes the remote function synchronously.
+  virtual void invokeFunction(
+      remote::RemoteFunctionResponse& response,
+      const remote::RemoteFunctionRequest& request) = 0;
+};
+
+/// Default implementation that wraps the actual thrift client.
+class ThriftRemoteFunctionClient : public IRemoteFunctionClient {
+ public:
+  explicit ThriftRemoteFunctionClient(
+      std::unique_ptr<RemoteFunctionClient> client)
+      : client_(std::move(client)) {}
+
+  void invokeFunction(
+      remote::RemoteFunctionResponse& response,
+      const remote::RemoteFunctionRequest& request) override {
+    client_->sync_invokeFunction(response, request);
+  }
+
+ private:
+  std::unique_ptr<RemoteFunctionClient> client_;
+};
+
+/// Factory function type for creating remote function clients.
+/// Parameters: location (socket address), eventBase (for async operations)
+/// Returns: A unique_ptr to an IRemoteFunctionClient implementation.
+using RemoteFunctionClientFactory = std::function<std::unique_ptr<
+    IRemoteFunctionClient>(folly::SocketAddress, folly::EventBase*)>;
+
 std::unique_ptr<RemoteFunctionClient> getThriftClient(
     folly::SocketAddress location,
     folly::EventBase* eventBase);
 
+/// Default factory that creates ThriftRemoteFunctionClient instances.
+inline std::unique_ptr<IRemoteFunctionClient> getDefaultRemoteFunctionClient(
+    folly::SocketAddress location,
+    folly::EventBase* eventBase) {
+  return std::make_unique<ThriftRemoteFunctionClient>(
+      getThriftClient(location, eventBase));
+}
+
 } // namespace facebook::velox::functions

velox/functions/remote/client/tests/RemoteFunctionTest.cpp

@@ -29,10 +29,13 @@
 #include "velox/functions/prestosql/StringFunctions.h"
 #include "velox/functions/prestosql/tests/utils/FunctionBaseTest.h"
 #include "velox/functions/remote/client/Remote.h"
+#include "velox/functions/remote/client/ThriftClient.h"
+#include "velox/functions/remote/if/GetSerde.h"
 #include "velox/functions/remote/if/gen-cpp2/RemoteFunctionService.h"
 #include "velox/functions/remote/server/RemoteFunctionService.h"
 #include "velox/functions/remote/utils/RemoteFunctionServiceProvider.h"
 #include "velox/serializers/PrestoSerializer.h"
+#include "velox/vector/VectorStream.h"
 
 using ::apache::thrift::ThriftServer;
 using ::facebook::velox::test::assertEqualVectors;
@@ -263,6 +266,133 @@ TEST_P(RemoteFunctionTest, connectionError) {
   }
 }
 
+/// Mock implementation of IRemoteFunctionClient for testing without a real
+/// thrift server.
+class MockRemoteFunctionClient : public IRemoteFunctionClient {
+ public:
+  MOCK_METHOD(
+      void,
+      invokeFunction,
+      (remote::RemoteFunctionResponse&, const remote::RemoteFunctionRequest&),
+      (override));
+};
+
+/// Test fixture that uses mock clients instead of a real thrift server running
+/// in the same process.
+class MockRemoteFunctionTest : public functions::test::FunctionBaseTest {
+ public:
+  void SetUp() override {
+    mockClient_ =
+        std::make_shared<testing::NiceMock<MockRemoteFunctionClient>>();
+  }
+
+  void TearDown() override {
+    mockClient_.reset();
+  }
+
+  /// Registers a remote function with a mock client factory.
+  void registerMockRemoteFunction(
+      const std::string& name,
+      std::vector<exec::FunctionSignaturePtr> signatures) {
+    RemoteThriftVectorFunctionMetadata metadata;
+    metadata.serdeFormat = remote::PageFormat::PRESTO_PAGE;
+    // Location doesn't matter since we're using a mock client.
+    metadata.location = folly::SocketAddress("127.0.0.1", 12345);
+
+    // Capture mockClient_ by value (shared_ptr) so it stays alive.
+    auto mockClientPtr = mockClient_;
+    metadata.clientFactory = [mockClientPtr](
+                                 folly::SocketAddress, folly::EventBase*) {
+      // We need this level of indirection because clientFactory returns a
+      // unique_ptr so we wouldn't have a reference to the mock client.
+      class MockClientWrapper : public IRemoteFunctionClient {
+       public:
+        explicit MockClientWrapper(
+            std::shared_ptr<MockRemoteFunctionClient> mock)
+            : mock_(std::move(mock)) {}
+
+        void invokeFunction(
+            remote::RemoteFunctionResponse& response,
+            const remote::RemoteFunctionRequest& request) override {
+          mock_->invokeFunction(response, request);
+        }
+
+       private:
+        std::shared_ptr<MockRemoteFunctionClient> mock_;
+      };
+      return std::make_unique<MockClientWrapper>(mockClientPtr);
+    };
+
+    registerRemoteFunction(name, std::move(signatures), metadata);
+  }
+
+  /// Helper to set up a mock response with a serialized result vector.
+  void setMockResponse(
+      remote::RemoteFunctionResponse& response,
+      const RowVectorPtr& resultVector) {
+    auto serde = getSerde(remote::PageFormat::PRESTO_PAGE);
+    auto result = response.result();
+    result->rowCount() = resultVector->size();
+    result->pageFormat() = remote::PageFormat::PRESTO_PAGE;
+    result->payload() = rowVectorToIOBuf(resultVector, *pool(), serde.get());
+  }
+
+ protected:
+  std::shared_ptr<testing::NiceMock<MockRemoteFunctionClient>> mockClient_;
+};
+
+TEST_F(MockRemoteFunctionTest, mockClientIsCalled) {
+  // Register a mock remote function.
+  auto signatures = {exec::FunctionSignatureBuilder()
+                         .returnType("bigint")
+                         .argumentType("bigint")
+                         .argumentType("bigint")
+                         .build()};
+  registerMockRemoteFunction("mock_plus", signatures);
+
+  // Set up the mock to return a valid response.
+  EXPECT_CALL(*mockClient_, invokeFunction(testing::_, testing::_))
+      .WillOnce([this](
+                    remote::RemoteFunctionResponse& response,
+                    const remote::RemoteFunctionRequest& /*request*/) {
+        // Return doubled values: input {1,2,3} + {1,2,3} = {2,4,6}
+        auto resultVector = makeRowVector({makeFlatVector<int64_t>({2, 4, 6})});
+        setMockResponse(response, resultVector);
+      });
+
+  auto inputVector = makeFlatVector<int64_t>({1, 2, 3});
+  auto results = evaluate<SimpleVector<int64_t>>(
+      "mock_plus(c0, c0)", makeRowVector({inputVector}));
+
+  // Verify the mock returned our expected values.
+  auto expected = makeFlatVector<int64_t>({2, 4, 6});
+  assertEqualVectors(expected, results);
+}
+
+TEST_F(MockRemoteFunctionTest, mockClientThrowsException) {
+  // Register a mock remote function.
+  auto signatures = {exec::FunctionSignatureBuilder()
+                         .returnType("bigint")
+                         .argumentType("bigint")
+                         .build()};
+  registerMockRemoteFunction("mock_throwing", signatures);
+
+  // Set up the mock to throw an exception.
+  EXPECT_CALL(*mockClient_, invokeFunction(testing::_, testing::_))
+      .WillOnce([](remote::RemoteFunctionResponse&,
+                   const remote::RemoteFunctionRequest&) {
+        throw std::runtime_error("Mock connection error");
+      });
+
+  auto inputVector = makeFlatVector<int64_t>({1, 2, 3});
+
+  // Verify the exception is propagated.
+  VELOX_ASSERT_THROW(
+      evaluate<SimpleVector<int64_t>>(
+          "mock_throwing(c0)", makeRowVector({inputVector})),
+      "Mock connection error");
+}
+
 VELOX_INSTANTIATE_TEST_SUITE_P(
     RemoteFunctionTestFixture,
     RemoteFunctionTest,