Testing templates (gtest)

#include <gtest/gtest.h>
#include <concepts>
#include <string>

template <typename T>
concept Animal = requires(T a) {
    { a.eats() } -> std::same_as<std::string>;
};

struct GrassEater {
    std::string eats() const { return "grass"; }
};
struct Cow : public GrassEater {};
struct Duck : public GrassEater {};

template <Animal T>
class GrassEaterTest : public ::testing::Test {
public:
    T grass_eater;
};

typedef ::testing::Types<Cow, Duck> GrassEaterTypes;
TYPED_TEST_SUITE(GrassEaterTest, GrassEaterTypes);

TYPED_TEST(GrassEaterTest, EatsGrass) {
    EXPECT_EQ(this->grass_eater.eats(), "grass");
}

$ apt install libgtest-dev
$ clang++ main.cpp --std=c++23 -lgtest -lgtest_main -pthread
$ ./a.out
[==========] Running 2 tests from 2 test suites.
[----------] Global test environment set-up.
[----------] 1 test from GrassEaterTest/0, where TypeParam = Cow
[ RUN      ] GrassEaterTest/0.EatsGrass
[       OK ] GrassEaterTest/0.EatsGrass (0 ms)
[----------] 1 test from GrassEaterTest/0 (0 ms total)

[----------] 1 test from GrassEaterTest/1, where TypeParam = Duck
[ RUN      ] GrassEaterTest/1.EatsGrass
[       OK ] GrassEaterTest/1.EatsGrass (0 ms)
[----------] 1 test from GrassEaterTest/1 (0 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 2 test suites ran. (0 ms total)
[  PASSED  ] 2 tests.