How to write ut for a complex algorithm

Question

I thought of writing ut for a complex algorithm, which consits of many steps. For example, the algorithm class like below. And I want to test every step. But it's obvious that i can process the private function. I am using the google gtest.

How shall I design the UT?

Class Algorithm
{private:
    PreProcess();
    Process();
    PostProcess();
}

Answer 1

There is a specific section in the Google Test documentation dealing with testing private code.

Short version is, try to avoid testing non-public functions. If you have to, then you can either change your class design, or your test can be made a friend of the class.

GTest provides a helper macro for this last option: FRIEND_TEST, but beware of namespace issues with this. Your test needs to be defined in the same namespace as the class being tested for this macro to work.

So something like:

#include <iostream>
#include "gtest/gtest.h"

class Algorithm {
 private:
  bool PreProcess() { std::cout << "Pre\n"; return true; }
  bool Process() { std::cout << "Process\n"; return true; }
  bool PostProcess() { std::cout << "Post\n"; return true; }
  FRIEND_TEST(AlgorithmPrivateTest, PreProcess);
  FRIEND_TEST(AlgorithmPrivateTest, Process);
  FRIEND_TEST(AlgorithmPrivateTest, PostProcess);
};

class AlgorithmPrivateTest : public testing::Test {
 protected:
  AlgorithmPrivateTest() : algorithm_() {}
  Algorithm algorithm_;
};

TEST_F(AlgorithmPrivateTest, PreProcess) {
  EXPECT_TRUE(algorithm_.PreProcess());
}

TEST_F(AlgorithmPrivateTest, Process) {
  EXPECT_TRUE(algorithm_.Process());
}

TEST_F(AlgorithmPrivateTest, PostProcess) {
  EXPECT_TRUE(algorithm_.PostProcess());
}

int main(int argc, char **argv) {
  testing::InitGoogleTest(&argc, argv);
  return RUN_ALL_TESTS();
}