Added the TCs for CopyFromBufferHandle scenario.

This was one of the TODO mentioned in the file.

tensorflow/lite/interpreter_test.cc

@@ -1164,9 +1164,16 @@ class TestDelegate : public ::testing::Test {
           [](TfLiteContext* context, TfLiteDelegate* delegate,
              TfLiteBufferHandle buffer_handle,
              TfLiteTensor* output) -> TfLiteStatus {
-        // TODO(ycling): Implement tests to test buffer copying logic.
+        TFLITE_CHECK_GE(buffer_handle, -1);
+        TFLITE_CHECK_EQ(output->buffer_handle, buffer_handle);
+        const float floats[] = {6., 6., 6.};
+        int num = output->dims->data[0];
+        for (int i = 0; i < num; i++) {
+          output->data.f[i] = floats[i];
+        }
         return kTfLiteOk;
       };
+
       delegate_.FreeBufferHandle =
           [](TfLiteContext* context, TfLiteDelegate* delegate,
              TfLiteBufferHandle* handle) { *handle = kTfLiteNullBufferHandle; };
@@ -1178,6 +1185,21 @@ class TestDelegate : public ::testing::Test {
     static TfLiteRegistration FakeFusedRegistration() {
       TfLiteRegistration reg = {nullptr};
       reg.custom_name = "fake_fused_op";
+
+      reg.invoke = [](TfLiteContext* context,
+                      TfLiteNode* node) -> TfLiteStatus {
+        // Copy input data to output data.
+        TfLiteTensor* a0 = &context->tensors[node->inputs->data[0]];
+        TfLiteTensor* a1 = &context->tensors[node->inputs->data[1]];
+        TfLiteTensor* out = &context->tensors[node->outputs->data[0]];
+        int num = a0->dims->data[0];
+        for (int i = 0; i < num; i++) {
+          out->data.f[i] = a0->data.f[i] + a1->data.f[i];
+        }
+        // Make the data stale so that CopyFromBufferHandle can be invoked
+        out->data_is_stale = true;
+        return kTfLiteOk;
+      };
       return reg;
     }
 
@@ -1320,6 +1342,64 @@ TEST_F(TestDelegate, ResizeInputWithNonDynamicDelegateShouldFail) {
   ASSERT_EQ(interpreter_->ResizeInputTensor(0, {1, 2}), kTfLiteError);
 }
 
+TEST_F(TestDelegate, TestCopyFromBufferInvoke) {
+  delegate_ = std::unique_ptr<SimpleDelegate>(new SimpleDelegate({0, 1, 2}));
+  TfLiteDelegate* delegate = delegate_->get_tf_lite_delegate();
+  interpreter_->ModifyGraphWithDelegate(delegate);
+
+  constexpr int kOutputTensorIndex = 3;
+  TfLiteTensor* tensor = interpreter_->tensor(kOutputTensorIndex);
+  std::vector<float> floats = {1.0f, 2.0f, 3.0f};
+  memcpy(interpreter_->typed_tensor<float>(0), floats.data(),
+         floats.size() * sizeof(float));
+
+  memcpy(interpreter_->typed_tensor<float>(1), floats.data(),
+         floats.size() * sizeof(float));
+
+  // Before setting the buffer handle, the tensor's `delegate` is already set
+  // because it will be written by the delegate.
+  ASSERT_EQ(tensor->delegate, delegate);
+  ASSERT_EQ(tensor->buffer_handle, kTfLiteNullBufferHandle);
+
+  // Called Invoke without setting the buffer will not call the CopyFromBuffer
+  interpreter_->Invoke();
+  std::vector<float> res = {2.0f, 4.0f, 6.0f};
+  for (int i = 0; i < tensor->dims->data[0]; ++i) {
+    ASSERT_EQ(tensor->data.f[i], res[i]);
+  }
+}
+
+TEST_F(TestDelegate, TestCopyFromBuffer) {
+  delegate_ = std::unique_ptr<SimpleDelegate>(new SimpleDelegate({0, 1, 2}));
+  TfLiteDelegate* delegate = delegate_->get_tf_lite_delegate();
+  interpreter_->ModifyGraphWithDelegate(delegate);
+
+  constexpr int kOutputTensorIndex = 3;
+  TfLiteTensor* tensor = interpreter_->tensor(kOutputTensorIndex);
+  std::vector<float> floats = {1.0f, 2.0f, 3.0f};
+  memcpy(interpreter_->typed_tensor<float>(0), floats.data(),
+         floats.size() * sizeof(float));
+
+  memcpy(interpreter_->typed_tensor<float>(1), floats.data(),
+         floats.size() * sizeof(float));
+
+  // Before setting the buffer handle, the tensor's `delegate` is already set
+  // because it will be written by the delegate.
+  ASSERT_EQ(tensor->delegate, delegate);
+  ASSERT_EQ(tensor->buffer_handle, kTfLiteNullBufferHandle);
+
+  TfLiteBufferHandle handle = AllocateBufferHandle();
+  TfLiteStatus status =
+      interpreter_->SetBufferHandle(kOutputTensorIndex, handle, delegate);
+  interpreter_->Invoke();
+  ASSERT_EQ(status, kTfLiteOk);
+  EXPECT_EQ(tensor->delegate, delegate);
+  EXPECT_EQ(tensor->buffer_handle, handle);
+  for (int i = 0; i < tensor->dims->data[0]; ++i) {
+    ASSERT_EQ(tensor->data.f[i], 6.0f);
+  }
+}
+
 class TestDelegateWithDynamicTensors : public ::testing::Test {
  protected:
   void SetUp() override {