Limit CPU usage in tests

Without these rules `ctest --parallel` would massively overuse
resources: With `N` being the number of CPU cores up to `N` CMake
instances would be spawned in parallel. Each of these CMake instances
would again spawn up to `N` build jobs. The resulting `N * N` job jobs
easily overload any CPU.

Author: hasselmm

tests/CMakeLists.txt

@@ -1,5 +1,9 @@
 include(platforms.cmake)
 
+cmake_host_system_information(RESULT _logical_cores QUERY NUMBER_OF_LOGICAL_CORES)
+set(CTEST_RESOURCE_SPEC_FILE "${CMAKE_BINARY_DIR}/CTestResources.json")
+configure_file(CTestResources.json.in "${CTEST_RESOURCE_SPEC_FILE}")
+
 function(arduino_cli_toolchain_add_test NAME)
     cmake_parse_arguments(_TEST "" "" "SKIP" ${ARGN})
 
@@ -36,6 +40,7 @@ function(arduino_cli_toolchain_add_test NAME)
         set_tests_properties(
             "${_test_name}/configure" PROPERTIES
             FIXTURES_SETUP "${_test_name}/configure"
+            RESOURCE_GROUPS "cpu-cores:1"
             DISABLED "${_test_disabled}"
             LABELS "${_board_name}")
 
@@ -52,6 +57,7 @@ function(arduino_cli_toolchain_add_test NAME)
             "${_test_name}/reconfigure" PROPERTIES
             FIXTURES_REQUIRED "${_test_name}/configure"
             FIXTURES_SETUP "${_test_name}/reconfigure"
+            RESOURCE_GROUPS "cpu-cores:1"
             DISABLED "${_test_disabled}"
             LABELS "${_board_name}")
 
@@ -63,6 +69,7 @@ function(arduino_cli_toolchain_add_test NAME)
         set_tests_properties(
             "${_test_name}/build" PROPERTIES
             FIXTURES_REQUIRED "${_test_name}/reconfigure"
+            RESOURCE_GROUPS "cpu-cores:${_logical_cores}"
             DISABLED "${_test_disabled}"
             LABELS "${_board_name}")
     endforeach()

tests/CTestResources.json.in

@@ -0,0 +1,6 @@
+{
+  "version": {"major": 1, "minor": 0},
+  "local": [{
+    "cpu-cores": [{"id": "0", "slots": ${_logical_cores} }]
+  }]
+}