message: Add some unit tests of the overload of InterpeterBuilder::operator()
  that takes an `int num_threads' parameter.
diff: @@ -267,6 +267,37 @@ TEST(BasicFlatBufferModel, TestModelInInterpreter) {
  }
  }
  +TEST(BasicFlatBufferModel, TestWithNumThreads) {
  + TestErrorReporter reporter;
  + auto model = FlatBufferModel::BuildFromFile(
  + "tensorflow/lite/testdata/test_model.bin", &reporter);
  + ASSERT_TRUE(model);
  + TrivialResolver resolver(&dummy_reg);
  + InterpreterBuilder builder(*model, resolver);
  +
  + std::unique_ptr<Interpreter> interpreter;
  + ASSERT_EQ(builder(&interpreter, /*num_threads=*/42), kTfLiteOk);
  + ASSERT_NE(interpreter, nullptr);
  + ASSERT_EQ(interpreter->subgraph(0)->context()->recommended_num_threads, 42);
  +
  + interpreter.reset();
  + ASSERT_EQ(builder(&interpreter, 0), kTfLiteOk);
  + ASSERT_NE(interpreter, nullptr);
  + ASSERT_EQ(interpreter->subgraph(0)->context()->recommended_num_threads, 0);
  +
  + interpreter.reset();
  + ASSERT_EQ(builder(&interpreter, -1), kTfLiteOk);
  + ASSERT_NE(interpreter, nullptr);
  + ASSERT_EQ(interpreter->subgraph(0)->context()->recommended_num_threads, -1);
  +
  + ASSERT_EQ(reporter.num_calls(), 0);
  + ASSERT_EQ(builder(&interpreter, -2), kTfLiteError);
  + ASSERT_EQ(reporter.num_calls(), 1);
  + ASSERT_PRED_FORMAT2(testing::IsSubstring,
  + "num_threads should be >= 0 or just -1",
  + reporter.error_messages());
  +}
  +
  // Test that loading a model with TensorFlow ops fails when the flex delegate is
  // not linked into the target.
  TEST(FlexModel, FailureWithoutFlexDelegate) {
  