Document test dependencies

While following README.md and trying to build && run official google tests I get this error /usr/bin/ld: cannot find -labsl::container collect2: error: ld returned 1 exit status

on make stage

What should I install in order to fix this and run tests?

uname -a 5.8.0-53-generic #60-Ubuntu SMP Thu May 6 07:46:32 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Hm... on another try it gives me this

-- Found Python: /usr/bin/python3.8 (found version "3.8.6") found components: Interpreter 
-- Configuring done
CMake Error at CMakeLists.txt:62 (add_executable):
  Target "robots-test" links to target "absl::container" but the target was
  not found.  Perhaps a find_package() call is missing for an IMPORTED
  target, or an ALIAS target is missing?

during cmake ..

found this in CMakeLists.txt.in

ExternalProject_Add(abseilcpp
    GIT_REPOSITORY https://github.com/abseil/abseil-cpp.git
    GIT_TAG master
    GIT_PROGRESS 1
    SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/abseil-cpp-src"
    BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/abseil-cpp-build"
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
    TEST_COMMAND ""
)

it's never a good idea to link to master branch of a git, should always pin version of your dependencies same goes for https://github.com/google/googletest.git

changing https://github.com/Folyd/robotstxt/blob/d46c028d63f15c52ec5ebd321db7782b7c033e81/tests/CMakeLists.txt.in

ExternalProject_Add(abseilcpp
    GIT_REPOSITORY https://github.com/abseil/abseil-cpp.git
    GIT_TAG 20200923.2
    GIT_PROGRESS 1
    SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/abseil-cpp-src"
    BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/abseil-cpp-build"
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
    TEST_COMMAND ""
)

ExternalProject_Add(googletest
    GIT_REPOSITORY https://github.com/google/googletest.git
    GIT_TAG release-1.10.0
    GIT_PROGRESS 1
    SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/gtest-src"
    BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/libs/gtest-build"
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
    TEST_COMMAND ""
)

changing https://github.com/Folyd/robotstxt/blob/d46c028d63f15c52ec5ebd321db7782b7c033e81/tests/CMakeLists.txt#L63 to target_link_libraries(robots-test absl::base absl::container absl::strings gtest_main dl)

and then building with LDFLAGS="-Wl,--no-as-needed" cmake ..

fixed an issue!