diff --git a/ptests/Makefile b/ptests/Makefile
index ed9fc23e85ff5da845b638f373736459bd67baca..b280e55b8a53f38ae794e38694c5f119e2b09d9a 100644
--- a/ptests/Makefile
+++ b/ptests/Makefile
@@ -1,27 +1,77 @@
-all: run-tests
+##########################################################################
+#                                                                        #
+#  This file is part of Frama-C.                                         #
+#                                                                        #
+#  Copyright (C) 2007-2020                                               #
+#    CEA (Commissariat à l'énergie atomique et aux énergies              #
+#         alternatives)                                                  #
+#                                                                        #
+#  you can redistribute it and/or modify it under the terms of the GNU   #
+#  Lesser General Public License as published by the Free Software       #
+#  Foundation, version 2.1.                                              #
+#                                                                        #
+#  It is distributed in the hope that it will be useful,                 #
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of        #
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         #
+#  GNU Lesser General Public License for more details.                   #
+#                                                                        #
+#  See the GNU Lesser General Public License version 2.1                 #
+#  for more details (enclosed in the file licenses/LGPLv2.1).            #
+#                                                                        #
+##########################################################################
 
-ptests.exe: purge-tests ptests.ml
+.PHONY: all
+all: ptests.exe
+
+.PHONY: ptests.exe
+ptests.exe:
 	dune build --root . ptests.exe
 
+.PHONY: clean
 clean: purge-tests
 	dune clean --root .
 
-.PHONY: run-tests clean-tests purge-tests tests
+##########################################################################
+
+TEST_DIRS= nothing cmd
+
+#######
+
+ENV_DIR=../_build/default/ptests/tests
 
 # removes also eventual broken dune files
+.PHONY: purge-tests
 purge-tests:
+	@echo "Purge tests"
 	find tests -name dune | grep -e "oracle.*/\|result.*/" | xargs --no-run-if-empty rm
 
+.PHONY: clean-tests
 clean-tests: purge-tests
-	rm -rf _build/default/ptests/tests
+	@echo "Clean tests"
+	rm -rf $(ENV_DIR)
+
+.PHONY: %.dune-file
+%.dune-file: purge-tests
+	@echo "Dune files for $(basename $@)"
+	dune exec --root . ./ptests.exe ./tests/$(basename $@)/tests
+	find ./tests/$(basename $@)/tests -name dune -print
+
+.PHONY: dune-files
+dune-files: $(addsuffix .dune-file,$(TEST_DIRS))
 
-TESTS= nothing cmd
-# opts
+# note: tests requires the package frama-c (even if frama-c is not used there)
+.PHONY: tests
+tests: dune-files
+	@echo "Run Tests..."
+	dune build $(addprefix @tests/,$(addsuffix /tests/ptests,$(TEST_DIRS)))
 
-run-tests: purge-tests
-	for dir in $(TESTS) ; do \
-	  dune exec --root . ./ptests.exe ./tests/$$dir/tests ; \
-	done
-	dune build $(addprefix @tests/,$(addsuffix /tests/ptests,$(TESTS)))
+.PHONY: tests
+force-tests: dune-files clean-tests
+	@echo "Run Tests..."
+	dune build $(addprefix @tests/,$(addsuffix /tests/ptests,$(TEST_DIRS)))
+	@echo "Nb .Log files:"
+	find $(ENV_DIR) -name \*.log -print | wc -l
+	@echo "Nb .err files:"
+	find $(ENV_DIR) -name \*.err -print | wc -l
 
-tests: run-tests
+##########################################################################