chore: bump catch to 2.13.6

chapters/projects/fetch.md

@@ -14,7 +14,7 @@ For example, to download Catch2:
 FetchContent_Declare(
   catch
   GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-  GIT_TAG        v2.13.0
+  GIT_TAG        v2.13.6
 )
 
 # CMake 3.14+

chapters/testing/catch.md

@@ -1,13 +1,42 @@
 # Catch
 
 
-Catch and [Catch2] (C++11 only version) are powerful, idomatic testing solutions similar in philosophy to PyTest for Python. To use Catch in a CMake project, there are several options.
+[Catch2] (C++11 only version) is a powerful, idomatic testing solutions similar in philosophy to PyTest for Python. It supports a wider range of compilers than GTest, and is quick to support new things, like M1 builds on macOS. It also has a smaller but faster twin, [doctest](https://github.com/onqtam/doctest), which is quick to compile but misses features like matchers. To use Catch in a CMake project, there are several options.
+
+## Configure methods
+
+Catch has nice CMake support, though to use it, you need the full repo. This could be with submodules or FetchContent. Both the [`extended-project`](https://gitlab.com/CLIUtils/modern-cmake/-/tree/master/examples/extended-project) and [`fetch`](https://gitlab.com/CLIUtils/modern-cmake/-/tree/master/examples/fetch) examples use FetchContent. See [the docs](https://github.com/catchorg/Catch2/blob/v2.x/docs/cmake-integration.md#top).
+
+## Quick download
+
+This is likely the simplest method and supports older versions of CMake. You can download the all-in-one header file in one step:
+
+```cmake
+add_library(catch_main main.cpp)
+target_include_directories(catch_main PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}")
+set(url https://github.com/philsquared/Catch/releases/download/v2.13.6/catch.hpp)
+file(
+  DOWNLOAD ${url} "${CMAKE_CURRENT_BINARY_DIR}/catch.hpp"
+  STATUS status
+  EXPECTED_HASH SHA256=681e7505a50887c9085539e5135794fc8f66d8e5de28eadf13a30978627b0f47)
+list(GET status 0 error)
+if(error)
+  message(FATAL_ERROR "Could not download ${url}")
+endif()
+target_include_directories(catch_main PUBLIC "${CMAKE_CURRENT_BINARY_DIR}")
+```
+
+This will two downloads when Catch 3 is released, as that now requires two files (but you no longer have to write a main.cpp). The `main.cpp` looks like this:
+
+```cpp
+#define CATCH_CONFIG_MAIN
+#include "catch.hpp"
+```
 
 ## Vendoring
 
 If you simply drop in the single include release of Catch into your project, this is what you would need to add Catch:
 
-
 ```cmake
 # Prepare "Catch" library for other executables
 set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/extern/catch)

chapters/testing/googletest.md

@@ -1,5 +1,7 @@
 # GoogleTest
 
+GoogleTest and GoogleMock are classic options; personally, I personally would recommend Catch2 instead, as GoogleTest heavily follows the Google development philosophy; it drops old compilers very quickly, it assumes users want to live at HEAD, etc. Adding GoogleMock is also often painful - and you need GoogleMock to get matchers, which are a default feature in Catch2 (but not doctest).
+
 ## Submodule method (preferred)
 
 To use this method, just checkout GoogleTest as a submodule:[^1]

examples/extended-project/tests/CMakeLists.txt

@@ -2,7 +2,7 @@
 FetchContent_Declare(
   catch
   GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-  GIT_TAG v2.9.1)
+  GIT_TAG v2.13.6)
 FetchContent_MakeAvailable(catch)
 # Adds Catch2::Catch2
 

examples/fetch/CMakeLists.txt

@@ -8,7 +8,7 @@ include(CTest)
 FetchContent_Declare(
   catch
   GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-  GIT_TAG v2.13.0)
+  GIT_TAG v2.13.6)
 
 # CMake 3.14+
 FetchContent_MakeAvailable(catch)