boost-ext/ut2

C++20 Unit-Testing library

---

"If you liked it then you "should have put a"_test on it", Beyonce rule

UT2: C++20 minimal/compile-time first unit-testing library

https://en.wikipedia.org/wiki/Unit_testing

Features

• Single header (https://raw.githubusercontent.com/boost-ext/ut2/main/ut2)
  • Easy integration (see FAQ)
• Compile-time first (executes tests at compile-time and/or run-time)
  • Detects memory leaks and UBs at compile-time*
• Explicit by design (no implicit conversions, narrowing, epsilon-less floating point comparisions, ...)
• Minimal API
• Reflection integration (optional via https://github.com/boost-ext/reflect)
• Compiles cleanly with (-fno-exceptions -fno-rtti -Wall -Wextra -Werror -pedantic -pedantic-errors)
• Fast compilation times (see compilation times)
• Fast run-time execution (see performance)
• Verifies itself upon include (aka run all tests via static_asserts but it can be disabled - see FAQ)

Based on the constexpr ability of given compiler/standard

Requirements

• C++20 (gcc-12+, clang-16+)

---

Examples

Hello world (https://godbolt.org/z/9d6PTEfbf)

#include <ut2>
#include <iostream> // output at run-time

constexpr auto sum(auto... args) { return (args + ...); }

int main() {
  using namespace ut;

  "sum"_test = [] {
    expect(sum(1) == 1_i);
    expect(sum(1, 2) == 3_i);
    expect(sum(1, 2, 3) == 6_i);
  };
}

$CXX example.cpp -std=c++20 -o example && ./example
PASSED: tests: 1 (1 passed, 0 failed, 1 compile-time), asserts: 3 (3 passed, 0 failed)

Execution model (https://godbolt.org/z/48PGjz3x9)

static_assert(("sum"_test = [] { // compile-time only
  expect(sum(1, 2, 3) == 6_i);
}));

int main() {
  "sum"_test = [] {              // compile time and run-time
    expect(sum(1, 2, 3) == 5_i);
  };

  "sum"_test = [] constexpr {    // compile-time and run-time
    expect(sum(1, 2, 3) == 6_i);
  };

  "sum"_test = [] mutable {      // run-time only
    expect(sum(1, 2, 3) == 6_i);
  };

  "sum"_test = [] consteval {    // compile-time only
    expect(sum(1, 2, 3) == 6_i);
  };
}

$CXX example.cpp -std=c++20 # -DUT_COMPILE_TIME_ONLY
ut2:156:25: error: static_assert((test(), "[FAILED]"));
example.cpp:13:44: note:"sum"_test
example.cpp:14:5:  note: in call to 'expect.operator()<ut::eq<int, int>>({6, 5})'

$CXX example.cpp -std=c++20 -o example -DUT_RUNTIME_ONLY && ./example
example.cpp:14:FAILED:"sum": 6 == 5
FAILED: tests: 3 (2 passed, 1 failed, 0 compile-time), asserts: 2 (1 passed, 1 failed)

Constant evaluation (https://godbolt.org/z/v1snWP5K3)

constexpr auto test() {
  if consteval { return 42; } else { return 87; }
}

int main() {
  "compile-time"_test = [] consteval {
    expect(42_i == test());
  };

  "run-time"_test = [] mutable {
    expect(87_i == test());
  };
}

$CXX example.cpp -std=c++20 -o example && ./example
PASSED: tests: 2 (2 passed, 0 failed, 1 compile-time), asserts: 1 (1 passed, 0 failed)

Suites/Sub-tests (https://godbolt.org/z/Mbzc9s3ad)

ut::suite test_suite = [] {
  "vector [sub-tests]"_test = [] {
    std::vector<int> v(5);
    expect(v.size() == 5_ul);
    expect(v.capacity() >= 5_ul);

    "resizing bigger changes size and capacity"_test = [=] {
      mut(v).resize(10);
      expect(v.size() == 10_ul);
      expect(v.capacity() >= 10_ul);
    };
  };
};

int main() { }

$CXX example.cpp -std=c++20 -o example && ./example
PASSED: tests: 2 (2 passed, 0 failed, 1 compile-time), asserts: 4 (4 passed, 0 failed)

Assertions (https://godbolt.org/z/W8qnMsrGo)

int main() {
  "expect"_test = [] {
    "different ways"_test = [] {
      expect(42_i == 42);
      expect(eq(42, 42))   << "same as expect(42_i == 42)";
      expect(_i(42) == 42) << "same as expect(42_i == 42)";
    };

    "floating point"_test = [] {
      expect((4.2 == 4.2_d)(.01)) << "floating point comparison with .01 epsilon precision";
    };

    "fatal"_test = [] mutable { // at run-time
      std::vector<int> v{1};
      expect[v.size() > 1_ul] << "fatal, aborts further execution";
      expect(v[1] == 42_i); // not executed
    };

    "compile-time expression"_test = [] {
      expect(constant<42 == 42_i>) << "requires compile-time expression";
    };
  };
}

$CXX example.cpp -std=c++20 -o example && ./example
example.cpp:21:FAILED:"fatal": 1 > 1
FAILED: tests: 3 (2 passed, 1 failed, 3 compile-time), asserts: 5 (4 passed, 1 failed)

Errors/Checks (https://godbolt.org/z/Tvnce9j4d)

int main() {
  "leak"_test = [] {
    new int; // compile-time error
  };

  "ub"_test = [] {
    int* i{};
    *i = 42; // compile-time error
  };

  "errors"_test = [] {
    expect(42_i == short(42)); // [ERROR] Comparision of different types is not allowed
    expect(42 == 42);          // [ERROR] Expression required: expect(42_i == 42)
    expect(4.2 == 4.2_d);      // [ERROR] Epsilon is required: expect((4.2 == 4.2_d)(.01))
  };
}

---

Reflection integration (https://godbolt.org/z/5T51odcfP)

int main() {
  struct foo { int a; int b; };
  struct bar { int a; int b; };

  "reflection"_test = [] {
    auto f = foo{.a=1, .b=2};
    expect(eq(foo{1, 2}, f));
    expect(members(foo{1, 2}) == members(f));
    expect(names(foo{}) == names(bar{}));
  };
};

$CXX example.cpp -std=c++20 -o example && ./example
PASSED: tests: 1 (1 passed, 0 failed, 1 compile-time), asserts: 3 (3 passed, 0 failed)

Custom configuration (https://godbolt.org/z/3qz5vG6nq)

struct outputter {
  template<ut::events::mode Mode>
  constexpr auto on(const ut::events::test_begin<Mode>&) { }
  template<ut::events::mode Mode>
  constexpr auto on(const ut::events::test_end<Mode>&) { }
  template<class TExpr>
  constexpr auto on(const ut::events::assert_pass<TExpr>&) { }
  template<class TExpr>
  constexpr auto on(const ut::events::assert_fail<TExpr>&) { }
  constexpr auto on(const ut::events::fatal&) { }
  constexpr auto on(const ut::events::summary&) { }
  template<class TMsg>
  constexpr auto on(const ut::events::log<TMsg>&) { }
};

struct custom_config {
  ::outputter outputter{};
  ut::reporter<decltype(outputter)> reporter{outputter};
  ut::runner<decltype(reporter)> runner{reporter};
};

template<>
auto ut::cfg<ut::override> = custom_config{};

int main() {
  "config"_test = [] mutable {
    expect(42 == 43_i); // no output
  };
};

$CXX example.cpp -std=c++20 -o example && ./example
echo $? # 139 # no output

---

Compilation times

Include - no iostream (https://raw.githubusercontent.com/boost-ext/ut2/main/ut2)

time $CXX -x c++ -std=c++20 ut2 -c -DNTEST          # 0.028s
time $CXX -x c++ -std=c++20 ut2 -c                  # 0.049s

Benchmark - 100 tests, 1000 asserts (https://godbolt.org/z/xhfc518xx)

[ut]:  time $CXX benchmark.cpp -std=c++20           # 0m13.498s
[ut2]: time $CXX benchmark.cpp -std=c++20           # 0m0.813s
[ut2]: time $CXX benchmark.cpp -std=c++20 -DNTEST   # 0m0.758s
-------------------------------------------------------------------------
[ut]  https://github.com/boost-ext/ut/releases/tag/v2.0.1
[ut2] https://github.com/boost-ext/ut2/releases/tag/v2.1.1

Performance

Benchmark - 100 tests, 1000 asserts (https://godbolt.org/z/6WzxvjEex)

time ./benchmark # 0m0.002s (-O3)
time ./benchmark # 0m0.013s (-g)

X86-64 assembly -O3 (https://godbolt.org/z/x6GYbs4hT)

int main() {
  "sum"_test = [] {
    expect(42_i == 42);
  };
}

main:
  mov  rax, qword ptr [rip + cfg<ut::override>+136]
  inc  dword ptr [rax + 24]
  mov  ecx, dword ptr [rax + 8]
  mov  edx, dword ptr [rax + 92]
  lea  esi, [rdx + 1]
  mov  dword ptr [rax + 92], esi
  mov  dword ptr [rax + 4*rdx + 28], ecx
  mov  rax, qword ptr [rax]
  lea  rcx, [rip + .L.str]
  mov  qword ptr [rax + 8], rcx
  mov  dword ptr [rax + 16], 6
  lea  rcx, [rip + template parameter object for fixed_string
  mov  qword ptr [rax + 24], rcx
  inc  dword ptr [rip + ut::v2_1_1::cfg<ut::v2_1_1::override>+52]
  mov  rax, qword ptr [rip + ut::cfg<ut::override>+136]
  mov  ecx, dword ptr [rax + 8]
  mov  edx, dword ptr [rax + 92]
  dec  edx
  mov  dword ptr [rax + 92], edx
  xor  esi, esi
  cmp  ecx, dword ptr [rax + 4*rdx + 28]
  sete sil
  inc  dword ptr [rax + 4*rsi + 16]
  xor  eax, eax
  ret

---

API

/**
 * Assert definition
 * @code
 * expect(42 == 42_i);
 * expect(42 == 42_i) << "log";
 * expect[42 == 42_i]; // fatal assertion, aborts further execution
 * @endcode
 */
inline constexpr struct {
  constexpr auto operator()(auto expr);
  constexpr auto operator[](auto expr);
} expect{};

/**
 * Test suite definition
 * @code
 * suite test_suite = [] { ... };
 * @encode
 */
struct suite;

/**
 * Test definition
 * @code
 * "foo"_test = []          { ... }; // compile-time and run-time
 * "foo"_test = [] mutable  { ... }; // run-time only
 * "foo"_test = [] constval { ... }; // compile-time only
 * @endcode
 */
template<fixed_string Str>
[[nodiscard]] constexpr auto operator""_test();

/**
 * Compile time expression
 * @code
 * expect(constant<42_i == 42>); // forces compile-time evaluation and run-time check
 * auto i = 0;
 * expect(constant<i == 42_i>);  // compile-time error
 * @encode
 */
template<auto Expr> inline constexpr auto constant;

/**
 * Allows mutating object (by default lambdas are immutable)
 * @code
 * "foo"_test = [] {
 *   int i = 0;
 *   "sub"_test = [i] {
 *     mut(i) = 42;
 *   };
 *   expect(i == 42_i);
 * };
 * @endcode
 */
template<class T> [[nodiscard]] constexpr auto& mut(const T&);

template<class TLhs, class TRhs> struct eq;  // equal
template<class TLhs, class TRhs> struct neq; // not equal
template<class TLhs, class TRhs> struct gt;  // greater
template<class TLhs, class TRhs> struct ge;  // greater equal
template<class TLhs, class TRhs> struct lt;  // less
template<class TLhs, class TRhs> struct le;  // less equal
template<class TLhs, class TRhs> struct nt;  // not

constexpr auto operator==(const auto& lhs, const auto& rhs) -> decltype(eq{lhs, rhs});
constexpr auto operator!=(const auto& lhs, const auto& rhs) -> decltype(neq{lhs, rhs});
constexpr auto operator> (const auto& lhs, const auto& rhs) -> decltype(gt{lhs, rhs});
constexpr auto operator>=(const auto& lhs, const auto& rhs) -> decltype(ge{lhs, rhs});
constexpr auto operator< (const auto& lhs, const auto& rhs) -> decltype(lt{lhs, rhs});
constexpr auto operator<=(const auto& lhs, const auto& rhs) -> decltype(le{lhs, rhs});
constexpr auto operator! (const auto& t)                    -> decltype(nt{t});

struct _b;      // bool (true_b = _b{true}, false_b = _b{false})
struct _c;      // char
struct _sc;     // signed char
struct _s;      // short
struct _i;      // int
struct _l;      // long
struct _ll;     // long long
struct _u;      // unsigned
struct _uc;     // unsigned char
struct _us;     // unsigned short
struct _ul;     // unsigned long
struct _ull;    // unsigned long long
struct _f;      // float
struct _d;      // double
struct _ld;     // long double
struct _i8;     // int8_t
struct _i16;    // int16_t
struct _i32;    // int32_t
struct _i64;    // int64_t
struct _u8;     // uint8_t
struct _u16;    // uint16_t
struct _u32;    // uint32_t
struct _u64;    // uint64_t
struct _string; // const char*

constexpr auto operator""_i(auto value)   -> decltype(_i(value));
constexpr auto operator""_s(auto value)   -> decltype(_s(value));
constexpr auto operator""_c(auto value)   -> decltype(_c(value));
constexpr auto operator""_sc(auto value)  -> decltype(_sc(value));
constexpr auto operator""_l(auto value)   -> decltype(_l(value));
constexpr auto operator""_ll(auto value)  -> decltype(_ll(value));
constexpr auto operator""_u(auto value)   -> decltype(_u(value));
constexpr auto operator""_uc(auto value)  -> decltype(_uc(value));
constexpr auto operator""_us(auto value)  -> decltype(_us(value));
constexpr auto operator""_ul(auto value)  -> decltype(_ul(value));
constexpr auto operator""_ull(auto value) -> decltype(_ull(value));
constexpr auto operator""_f(auto value)   -> decltype(_f(value));
constexpr auto operator""_d(auto value)   -> decltype(_d(value));
constexpr auto operator""_ld(auto value)  -> decltype(_ld(value));
constexpr auto operator""_i8(auto value)  -> decltype(_i8(value));
constexpr auto operator""_i16(auto value) -> decltype(_i16(value));
constexpr auto operator""_i32(auto value) -> decltype(_i32(value));
constexpr auto operator""_i64(auto value) -> decltype(_i64(value));
constexpr auto operator""_u8(auto value)  -> decltype(_u8(value));
constexpr auto operator""_u16(auto value) -> decltype(_u16(value));
constexpr auto operator""_u32(auto value) -> decltype(_u32(value));
constexpr auto operator""_u64(auto value) -> decltype(_u64(value));

template<fixed_string Str>
[[nodiscard]] constexpr auto operator""_s() -> decltype(_string(Str));

Configuration

namespace events {
enum class mode {
  run_time,
  compile_time
};

template<mode Mode>
struct test_begin {
  const char* file_name{};
  int line{}; const char* name{};
};

template<mode Mode>
struct test_end {
  const char* file_name{};
  int line{};
  const char* name{};
  enum { FAILED, PASSED, COMPILE_TIME } result{};
};

template<class TExpr>
struct assert_pass {
  const char* file_name{};
  int line{};
  TExpr expr{};
};

template<class TExpr>
struct assert_fail {
  const char* file_name{};
  int line{};
  TExpr expr{};
};

struct fatal { };

template<class TMsg>
struct log {
  const TMsg& msg;
  bool result{};
};

struct summary {
  enum { FAILED, PASSED, COMPILE_TIME };
  unsigned asserts[2]{}; /* FAILED, PASSED */
  unsigned tests[3]{}; /* FAILED, PASSED, COMPILE_TIME */
};
} // namespace events

struct outputter {
  template<events::mode Mode> constexpr auto on(const events::test_begin<Mode>&);
  constexpr auto on(const events::test_begin<events::mode::run_time>& event);
  template<events::mode Mode> constexpr auto on(const events::test_end<Mode>&);
  template<class TExpr> constexpr auto on(const events::assert_pass<TExpr>&);
  template<class TExpr> constexpr auto on(const events::assert_fail<TExpr>&);
  constexpr auto on(const events::fatal&);
  template<class TMsg> constexpr auto on(const events::log<TMsg>&);
  constexpr auto on(const events::summary& event);
};

struct reporter {
  constexpr auto on(const events::test_begin<events::mode::run_time>&);
  constexpr auto on(const events::test_end<events::mode::run_time>&);
  constexpr auto on(const events::test_begin<events::mode::compile_time>&);
  constexpr auto on(const events::test_end<events::mode::compile_time>&);
  template<class TExpr> constexpr auto on(const events::assert_pass<TExpr>&);
  template<class TExpr> constexpr auto on(const events::assert_fail<TExpr>&);
  constexpr auto on(const events::fatal& event);
};

struct runner {
  template<class Test> constexpr auto on(Test test) -> bool;
};

/**
 * Customization point to override the default configuration
 * @code
 * template<class... Ts> auto ut::cfg<ut::override, Ts...> = my_config{};
 * @endcode
 */
struct override { }; /// to override configuration by users
struct default_cfg;  /// default configuration
template <class...> inline auto cfg = default_cfg{};

#define UT2 2'1'1               // Current library version (SemVer)
#define UT_RUN_TIME_ONLY        // If defined tests will be executed
                                // at run-time + static_assert tests
#define UT_COMPILE_TIME_ONLY    // If defined only compile-time tests
                                // will be executed
#define NTEST                   // If defined it disables running
                                // static_asserts tests for the UT library
                                // (user tests are not affected)

---

FAQ

• How does UT2 compare to https://github.com/boost-ext/ut?

  UT2 ideas are based on UT. UT2 aim is not to replace UT. UT2 is minimal (no STL required). UT2 has different execution model (can run tests at compile-time and/or run-time).

• Can I disable running tests at compile-time for faster compilation times?

  When NTEST is defined static_asserts tests won't be executed upon inclusion. Note: Use with caution as disabling tests means that there are no guarantees upon inclusion that the given compiler/env combination works as expected.

• How to integrate with CMake/CPM?

  CPMAddPackage(
    Name ut2
    GITHUB_REPOSITORY boost-ext/ut2
    GIT_TAG v2.1.1
  )
  add_library(ut2 INTERFACE)
  target_include_directories(ut2 SYSTEM INTERFACE ${ut2_SOURCE_DIR})
  add_library(ut2::ut2 ALIAS ut2)
  

  target_link_libraries(${PROJECT_NAME} ut2::ut2);
  

• Similar projects?

  ut, catch2, googletest, gunit, boost.test