Important

We're excited you're checking out Hegel! Hegel is in beta, and we'd love for you to try it and report any feedback.

As part of our beta, we may make breaking changes if it makes Hegel a better property-based testing library. If that instability bothers you, please check back in a few months for a stable release!

See https://hegel.dev/compatibility for more details.

Hegel for C++

• Documentation
• Website

Hegel is a property-based testing library for C++. Hegel is based on Hypothesis, using the Hegel protocol.

Installation

Hegel requires C++20.

To install with CMake, add this to your CMakeLists.txt (CMake 3.14+ required):

include(FetchContent)
FetchContent_Declare(
    hegel
    GIT_REPOSITORY https://github.com/hegeldev/hegel-cpp.git
    GIT_TAG v0.6.2
)
FetchContent_MakeAvailable(hegel)

target_link_libraries(your_target PRIVATE hegel)

At configure time the build downloads a small prebuilt shared library (libhegel, Hegel's native engine) for your platform and verifies it against its published SHA-256, then links it. To link a locally built engine instead, pass -DHEGEL_LIBHEGEL_LIBRARY=/path/to/libhegel_c.<ext>. See https://hegel.dev/reference/installation for details.

Quickstart

Here's a quick example of how to write a Hegel test:

#include <hegel/hegel.h>
#include <algorithm>
#include <stdexcept>
#include <vector>

namespace gs = hegel::generators;

std::vector<int> my_sort(std::vector<int> ls) {
    std::sort(ls.begin(), ls.end());
    ls.erase(std::unique(ls.begin(), ls.end()), ls.end());
    return ls;
}

HEGEL_TEST(sort_agrees_with_std_sort)(hegel::TestCase& tc) {
    auto vec1 = tc.draw(gs::vectors(gs::integers<int>()));
    auto vec2 = my_sort(vec1);
    std::sort(vec1.begin(), vec1.end());
    if (vec1 != vec2) {
        throw std::runtime_error("sort mismatch");
    }
}

int main() {
    sort_agrees_with_std_sort();
    return 0;
}

HEGEL_TEST defines the test as a plain function you can invoke from main() or from any test framework, and names the test in Hegel's example database so failures found in one run are replayed first in the next. (You can also call hegel::test(callback, settings) directly.)

This test will fail! Hegel will produce a minimal failing test case for us:

Generated: [0,0]
libc++abi: terminating due to uncaught exception of type std::runtime_error:
Hegel test failed: sort mismatch

Hegel reports the minimal example showing that our sort is incorrectly dropping duplicates.