192 lines
6.4 KiB
Markdown
192 lines
6.4 KiB
Markdown
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<a id="top"></a>
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# Known limitations
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Over time, some limitations of Catch2 emerged. Some of these are due
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to implementation details that cannot be easily changed, some of these
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are due to lack of development resources on our part, and some of these
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are due to plain old 3rd party bugs.
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## Implementation limits
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### Sections nested in loops
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If you are using `SECTION`s inside loops, you have to create them with
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different name per loop's iteration. The recommended way to do so is to
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incorporate the loop's counter into section's name, like so:
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```cpp
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TEST_CASE( "Looped section" ) {
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for (char i = '0'; i < '5'; ++i) {
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SECTION(std::string("Looped section ") + i) {
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SUCCEED( "Everything is OK" );
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}
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}
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}
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```
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or with a `DYNAMIC_SECTION` macro (that was made for exactly this purpose):
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```cpp
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TEST_CASE( "Looped section" ) {
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for (char i = '0'; i < '5'; ++i) {
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DYNAMIC_SECTION( "Looped section " << i) {
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SUCCEED( "Everything is OK" );
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}
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}
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}
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```
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### Tests might be run again if last section fails
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If the last section in a test fails, it might be run again. This is because
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Catch2 discovers `SECTION`s dynamically, as they are about to run, and
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if the last section in test case is aborted during execution (e.g. via
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the `REQUIRE` family of macros), Catch2 does not know that there are no
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more sections in that test case and must run the test case again.
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### MinGW/CygWin compilation (linking) is extremely slow
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Compiling Catch2 with MinGW can be exceedingly slow, especially during
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the linking step. As far as we can tell, this is caused by deficiencies
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in its default linker. If you can tell MinGW to instead use lld, via
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`-fuse-ld=lld`, the link time should drop down to reasonable length
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again.
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## Features
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This section outlines some missing features, what is their status and their possible workarounds.
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### Thread safe assertions
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Catch2's assertion macros are not thread safe. This does not mean that
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you cannot use threads inside Catch's test, but that only single thread
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can interact with Catch's assertions and other macros.
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This means that this is ok
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```cpp
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std::vector<std::thread> threads;
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std::atomic<int> cnt{ 0 };
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for (int i = 0; i < 4; ++i) {
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threads.emplace_back([&]() {
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++cnt; ++cnt; ++cnt; ++cnt;
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});
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}
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for (auto& t : threads) { t.join(); }
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REQUIRE(cnt == 16);
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```
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because only one thread passes the `REQUIRE` macro and this is not
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```cpp
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std::vector<std::thread> threads;
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std::atomic<int> cnt{ 0 };
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for (int i = 0; i < 4; ++i) {
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threads.emplace_back([&]() {
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++cnt; ++cnt; ++cnt; ++cnt;
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CHECK(cnt == 16);
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});
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}
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for (auto& t : threads) { t.join(); }
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REQUIRE(cnt == 16);
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```
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We currently do not plan to support thread-safe assertions.
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### Process isolation in a test
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Catch does not support running tests in isolated (forked) processes. While this might in the future, the fact that Windows does not support forking and only allows full-on process creation and the desire to keep code as similar as possible across platforms, mean that this is likely to take significant development time, that is not currently available.
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### Running multiple tests in parallel
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Catch2 keeps test execution in one process strictly serial, and there
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are no plans to change this. If you find yourself with a test suite
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that takes too long to run and you want to make it parallel, you have
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to run multiple processes side by side.
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There are 2 basic ways to do that,
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* you can split your tests into multiple binaries, and run those binaries
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in parallel
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* you can run the same test binary multiple times, but run a different
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subset of the tests in each process
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There are multiple ways to achieve the latter, the easiest way is to use
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[test sharding](command-line.md#test-sharding).
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## 3rd party bugs
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This section outlines known bugs in 3rd party components (this means compilers, standard libraries, standard runtimes).
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### Visual Studio 2017 -- raw string literal in assert fails to compile
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There is a known bug in Visual Studio 2017 (VC 15), that causes compilation
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error when preprocessor attempts to stringize a raw string literal
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(`#` preprocessor directive is applied to it). This snippet is sufficient
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to trigger the compilation error:
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```cpp
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#include <catch2/catch_test_macros.hpp>
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TEST_CASE("test") {
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CHECK(std::string(R"("\)") == "\"\\");
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}
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```
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Catch2 provides a workaround, by letting the user disable stringification
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of the original expression by defining `CATCH_CONFIG_DISABLE_STRINGIFICATION`,
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like so:
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```cpp
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#define CATCH_CONFIG_DISABLE_STRINGIFICATION
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#include <catch2/catch_test_macros.hpp>
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TEST_CASE("test") {
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CHECK(std::string(R"("\)") == "\"\\");
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}
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```
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_Do note that this changes the output:_
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```
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catchwork\test1.cpp(6):
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PASSED:
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CHECK( Disabled by CATCH_CONFIG_DISABLE_STRINGIFICATION )
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with expansion:
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""\" == ""\"
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```
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### Clang/G++ -- skipping leaf sections after an exception
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Some versions of `libc++` and `libstdc++` (or their runtimes) have a bug with `std::uncaught_exception()` getting stuck returning `true` after rethrow, even if there are no active exceptions. One such case is this snippet, which skipped the sections "a" and "b", when compiled against `libcxxrt` from the master branch
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```cpp
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#include <catch2/catch_test_macros.hpp>
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TEST_CASE("a") {
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CHECK_THROWS(throw 3);
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}
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TEST_CASE("b") {
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int i = 0;
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SECTION("a") { i = 1; }
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SECTION("b") { i = 2; }
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CHECK(i > 0);
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}
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```
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If you are seeing a problem like this, i.e. weird test paths that trigger only under Clang with `libc++`, or only under very specific version of `libstdc++`, it is very likely you are seeing this. The only known workaround is to use a fixed version of your standard library.
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### Visual Studio 2022 -- can't compile assertion with the spaceship operator
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[The C++ standard requires that `std::foo_ordering` is only comparable with
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a literal 0](https://eel.is/c++draft/cmp#categories.pre-3). There are
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multiple strategies a stdlib implementation can take to achieve this, and
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MSVC's STL has changed the strategy they use between two releases of VS 2022.
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With the new strategy, `REQUIRE((a <=> b) == 0)` no longer compiles under
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MSVC. Note that Catch2 can compile code using MSVC STL's new strategy,
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but only when compiled with a C++20 conforming compiler. MSVC is currently
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not conformant enough, but `clang-cl` will compile the assertion above
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using MSVC STL without problem.
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This change got in with MSVC v19.37](https://godbolt.org/z/KG9obzdvE).
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