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external/Catch2/README.md

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+<a id="top"></a>
+![Catch2 logo](data/artwork/catch2-logo-small-with-background.png)
+
+[![Github Releases](https://img.shields.io/github/release/catchorg/catch2.svg)](https://github.com/catchorg/catch2/releases)
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+[![Build Status](https://ci.appveyor.com/api/projects/status/github/catchorg/Catch2?svg=true&branch=devel)](https://ci.appveyor.com/project/catchorg/catch2)
+[![Code Coverage](https://codecov.io/gh/catchorg/Catch2/branch/devel/graph/badge.svg)](https://codecov.io/gh/catchorg/Catch2)
+[![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://godbolt.org/z/EdoY15q9G)
+[![Join the chat in Discord: https://discord.gg/4CWS9zD](https://img.shields.io/badge/Discord-Chat!-brightgreen.svg)](https://discord.gg/4CWS9zD)
+
+
+## What is Catch2?
+
+Catch2 is mainly a unit testing framework for C++, but it also
+provides basic micro-benchmarking features, and simple BDD macros.
+
+Catch2's main advantage is that using it is both simple and natural.
+Test names do not have to be valid identifiers, assertions look like
+normal C++ boolean expressions, and sections provide a nice and local way
+to share set-up and tear-down code in tests.
+
+**Example unit test**
+```cpp
+#include <catch2/catch_test_macros.hpp>
+
+#include <cstdint>
+
+uint32_t factorial( uint32_t number ) {
+    return number <= 1 ? number : factorial(number-1) * number;
+}
+
+TEST_CASE( "Factorials are computed", "[factorial]" ) {
+    REQUIRE( factorial( 1) == 1 );
+    REQUIRE( factorial( 2) == 2 );
+    REQUIRE( factorial( 3) == 6 );
+    REQUIRE( factorial(10) == 3'628'800 );
+}
+```
+
+**Example microbenchmark**
+```cpp
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/benchmark/catch_benchmark.hpp>
+
+#include <cstdint>
+
+uint64_t fibonacci(uint64_t number) {
+    return number < 2 ? number : fibonacci(number - 1) + fibonacci(number - 2);
+}
+
+TEST_CASE("Benchmark Fibonacci", "[!benchmark]") {
+    REQUIRE(fibonacci(5) == 5);
+
+    REQUIRE(fibonacci(20) == 6'765);
+    BENCHMARK("fibonacci 20") {
+        return fibonacci(20);
+    };
+
+    REQUIRE(fibonacci(25) == 75'025);
+    BENCHMARK("fibonacci 25") {
+        return fibonacci(25);
+    };
+}
+```
+
+_Note that benchmarks are not run by default, so you need to run it explicitly
+with the `[!benchmark]` tag._
+
+
+## Catch2 v3 has been released!
+
+You are on the `devel` branch, where the v3 version is being developed.
+v3 brings a bunch of significant changes, the big one being that Catch2
+is no longer a single-header library. Catch2 now behaves as a normal
+library, with multiple headers and separately compiled implementation.
+
+The documentation is slowly being updated to take these changes into
+account, but this work is currently still ongoing.
+
+For migrating from the v2 releases to v3, you should look at [our
+documentation](docs/migrate-v2-to-v3.md#top). It provides a simple
+guidelines on getting started, and collects most common migration
+problems.
+
+For the previous major version of Catch2 [look into the `v2.x` branch
+here on GitHub](https://github.com/catchorg/Catch2/tree/v2.x).
+
+
+## How to use it
+This documentation comprises these three parts:
+
+* [Why do we need yet another C++ Test Framework?](docs/why-catch.md#top)
+* [Tutorial](docs/tutorial.md#top) - getting started
+* [Reference section](docs/Readme.md#top) - all the details
+
+
+## More
+* Issues and bugs can be raised on the [Issue tracker on GitHub](https://github.com/catchorg/Catch2/issues)
+* For discussion or questions please use [our Discord](https://discord.gg/4CWS9zD)
+* See who else is using Catch2 in [Open Source Software](docs/opensource-users.md#top)
+or [commercially](docs/commercial-users.md#top).