mkdir temp
cd temp
cmake ..
make
../bin/alpha

Find the latest Catch2 release, and download both amalgamation files (.hpp and .cpp) and place them in /alpha/tests/

cd tests
wget {catch_amalgamated.cpp} .
wget {catch_amalgamated.hpp} .

Then to run the tests, build with -DBUILD_TEST=ON, then run /alpha/bin/runTests

cd temp
cmake .. -DBUILD_TESTS=ON
make
../bin/runTests