How to Test Projection Functions Independently in C++

Testing projection functions independently of the algorithms that use them is a good practice to ensure that each function behaves correctly in isolation.

This approach can simplify debugging and improve the reliability of your code.

Steps for Testing Projection Functions:

1. Define Test Cases: Identify different scenarios and edge cases that your projection function should handle.
2. Use Test Frameworks: Utilize a C++ testing framework like Google Test or Catch2 to write and organize your test cases.
3. Isolate the Function: Test the projection function by passing controlled inputs and verifying the outputs.

Example with Google Test:

First, install Google Test and set up your testing environment. Then, write test cases for your projection function. Assume we have a projection function that returns the Level of a Player:

1#include <gtest/gtest.h>
2#include <vector>
3
4struct Player {
5  std::string Name;
6  int Level;
7};
8
9int getLevel(const Player& P) {
10  return P.Level;
11}
12
13TEST(ProjectionFunctionTest, HandlesPositiveLevels) {
14  Player P{"Legolas", 49};
15  EXPECT_EQ(getLevel(P), 49);
16}
17
18TEST(ProjectionFunctionTest, HandlesNegativeLevels) {
19  Player P{"Gimli", -10};
20  EXPECT_EQ(getLevel(P), -10);
21}
22
23TEST(ProjectionFunctionTest, HandlesZeroLevel) {
24  Player P{"Gandalf", 0};
25  EXPECT_EQ(getLevel(P), 0);
26}
27
28int main(int argc, char **argv) {
29  ::testing::InitGoogleTest(&argc, argv);
30  return RUN_ALL_TESTS();
31}

Running the Tests:

Compile and run your tests using the Google Test framework:

1g++ -std=c++17 -lgtest -lgtest_main -pthread test_projection.cpp -o test_projection
2./test_projection

Example with Catch2:

Alternatively, you can use Catch2 for a simpler setup:

1#define CATCH_CONFIG_MAIN
2#include <catch2/catch.hpp>
3#include <vector>
4
5struct Player {
6  std::string Name;
7  int Level;
8};
9
10int getLevel(const Player& P) {
11  return P.Level;
12}
13
14TEST_CASE("getLevel returns the correct level") {
15  Player P1{"Legolas", 49};
16  Player P2{"Gimli", -10};
17  Player P3{"Gandalf", 0};
18
19  REQUIRE(getLevel(P1) == 49);
20  REQUIRE(getLevel(P2) == -10);
21  REQUIRE(getLevel(P3) == 0);
22}

Running the Tests:

Compile and run your tests with Catch2:

1g++ -std=c++17 test_projection.cpp -o test_projection
2./test_projection

Key Points:

• Isolation: Ensure that the projection function is tested in isolation from the algorithm.
• Test Cases: Cover a range of inputs, including edge cases.
• Frameworks: Use testing frameworks like Google Test or Catch2 for structured and automated testing.

By testing projection functions independently, you can verify their correctness and ensure they handle all expected scenarios, leading to more robust and reliable code.