Don't interleave output from test suite when running under gmake4 or

newer.

On gmake 3, warn the user

Makefile

@@ -21,7 +21,9 @@ MAKEFLAGS += --no-builtin-rules
 # GNU Make earlier than 4.0 don't have the output-sync option, but we need it
 # to make parallel simulator test output readable. (otherwise it gets interleaved)
 ifeq ($(shell test $(firstword $(subst ., ,$(MAKE_VERSION))) -ge 4; echo $$?),0)
-SUBDIR_MAKEFLAGS+=--output-sync=target
+MAKEFLAGS+=--output-sync=target
+else
+_using_old_make=1
 endif
 
 include $(dir $(abspath $(lastword $(MAKEFILE_LIST))))/etc/makefiles/arduino-cli.mk
@@ -73,6 +75,9 @@ update:
 		git submodule update --init --recursive
 
 simulator-tests:
+ifneq ($(_using_old_make),)
+	$(info You're using an older version of GNU Make that doesn't offer the --output-sync option. If you're running the test suite in parallel, output may be garbled. You might consider using GNU Make 4.0 or later instead)
+endif
 	$(MAKE) -C tests all
 
 docker-simulator-tests:

testing/makefiles/testcase.mk

@@ -69,6 +69,7 @@ build: $(if $(HAS_KTEST_FILE), generate-testcase) compile-sketch
 all: run
 
 run: ${BIN_DIR}/${BIN_FILE}
+	$(info )
 	$(info Running test $(testcase))
 	$(QUIET) "${BIN_DIR}/${BIN_FILE}" -t -q
 

tests/Makefile

@@ -36,6 +36,10 @@ TESTS		:= $(shell cd $(tests_dir); find ${TEST_PATH} -name '*.ino' -exec dirname
 
 KALEIDOSCOPE_CCACHE = 1
 
+# The clutter up the test output on Make 4.0 and newer
+MAKEFLAGS += --no-print-directory
+
+
 include $(top_dir)/etc/makefiles/arduino-cli.mk
 
 # If we start off in tests to run make all, the sketch makefiles guess the wrong location for