To use the Catch2 library, we will modify CMakeLists.txt from the previous recipe, to perform the following steps:

1. We can keep most of CMakeLists.txt unchanged:

# set minimum cmake version
cmake_minimum_required(VERSION 3.5 FATAL_ERROR)

# project name and language
project(recipe-02 LANGUAGES CXX)

# require C++11
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

# example library
add_library(sum_integers sum_integers.cpp)

# main code
add_executable(sum_up main.cpp)
target_link_libraries(sum_up sum_integers)

# testing binary
add_executable(cpp_test test.cpp)
target_link_libraries(cpp_test sum_integers)

2. The only change, with respect to the previous recipe, is to remove all of the tests except for one, and rename it (to make clear what we have changed). Note that we pass the --success option to our unit tests executable. This is a Catch2 option, and will produce output from tests, even upon success:

enable_testing()

add_test(
  NAME catch_test
  COMMAND $<TARGET_FILE:cpp_test> --success
  )

3. That's it! Let us configure, build, and test. The tests will be run using the -VV option in CTest, to get output from the unit tests executable:

$ mkdir -p build
$ cd build
$ cmake ..
$ cmake --build .
$ ctest -V

UpdateCTestConfiguration from :/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/build/DartConfiguration.tcl
UpdateCTestConfiguration from :/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/build/DartConfiguration.tcl
Test project /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/build
Constructing a list of tests
Done constructing a list of tests
Updating test list for fixtures
Added 0 tests to meet fixture requirements
Checking test dependency graph...
Checking test dependency graph end
test 1
 Start 1: catch_test

1: Test command: /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/build/cpp_test "--success"
1: Test timeout computed to be: 10000000
1: 
1: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1: cpp_test is a Catch v2.0.1 host application.
1: Run with -? for options
1: 
1: ----------------------------------------------------------------
1: Sum of integers for a short vector
1: ----------------------------------------------------------------
1: /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:10
1: ...................................................................
1: 
1: /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:12: 
1: PASSED:
1: REQUIRE( sum_integers(integers) == 15 )
1: with expansion:
1: 15 == 15
1: 
1: ----------------------------------------------------------------
1: Sum of integers for a longer vector
1: ----------------------------------------------------------------
1: /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:15
1: ...................................................................
1: 
1: /home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:20: 
1: PASSED:
1: REQUIRE( sum_integers(integers) == 500500 )
1: with expansion:
1: 500500 (0x7a314) == 500500 (0x7a314)
1: 
1: ===================================================================
1: All tests passed (2 assertions in 2 test cases)
1:
1/1 Test #1: catch_test ....................... Passed 0.00 s

100% tests passed, 0 tests failed out of 1

Total Test time (real) = 0.00 sec

4. We can also try the cpp_test binary directly, and can see output directly from Catch2:

$ ./cpp_test --success

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cpp_test is a Catch v2.0.1 host application.
Run with -? for options

-------------------------------------------------------------------
Sum of integers for a short vector
-------------------------------------------------------------------
/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:10
...................................................................

/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:12: 
PASSED:
  REQUIRE( sum_integers(integers) == 15 )
with expansion:
  15 == 15

-------------------------------------------------------------------
Sum of integers for a longer vector
-------------------------------------------------------------------
/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:15
...................................................................

/home/user/cmake-cookbook/chapter-04/recipe-02/cxx-example/test.cpp:20: 
PASSED:
  REQUIRE( sum_integers(integers) == 500500 )
with expansion:
  500500 (0x7a314) == 500500 (0x7a314)

===================================================================
All tests passed (2 assertions in 2 test cases)

5. Catch will generate an executable with a command-line interface. We invite you to  also try to execute the following command to explore the options offered by the unit testing framework:

$ ./cpp_test --help