Introduce a CMake WITH_TESTS option

To enable or disable tests in the build step and to circumvent the
CUnit build dependency.

Signed-off-by: Kai Buschulte <kai.buschulte@cedalo.com>

CMakeLists.txt

@@ -33,6 +33,7 @@ option(WITH_BUNDLED_DEPS "Build with bundled dependencies?" ON)
 option(WITH_TLS "Include SSL/TLS support?" ON)
 option(WITH_TLS_PSK "Include TLS-PSK support (requires WITH_TLS)?" ON)
 option(WITH_EC "Include Elliptic Curve support (requires WITH_TLS)?" ON)
+option(WITH_TESTS "Enable tests" ON)
 if (WITH_TLS)
 	find_package(OpenSSL REQUIRED)
 	add_definitions("-DWITH_TLS")
@@ -162,6 +163,7 @@ install(FILES "${CMAKE_CURRENT_BINARY_DIR}/libmosquittopp.pc" DESTINATION "${CMA
 # ========================================
 # Testing
 # ========================================
-enable_testing()
-
-add_subdirectory(test)
+if(WITH_TESTS)
+	enable_testing()
+	add_subdirectory(test)
+endif()