[tests] access to the local cache wp

tests/dune

+(rule
+ (target "path-to-wp-cache")
+ (action (run %{dep:./set-path-to-wp-cache.sh})))

tests/set-path-to-wp-cache.sh

+#!/bin/sh
+pwd -P | sed 's:\(.*\)/_build/[^/]*\(/.*$\):\1\2/wp-cache:' > path-to-wp-cache
+echo "MetaACSL: using WP cache dir:"
+cat path-to-wp-cache

tests/test_config

+# note: the file @WP_CACHE@ must contain an absolute path to the source
+#       worktree 'tests/wp-cache'. This is done in a rule of 'tests/dune' file.
+MACRO: WP_CACHE ../../../tests/path-to-wp-cache
+
 MACRO: META -meta
-MACRO: WP -then-last -wp -wp-timeout 1 -wp-par 1 -wp-msg-key shell  -wp-cache update -wp-session @PTEST_SUITE_DIR@/../wp-cache
+MACRO: WP -then-last -wp -wp-timeout 1 -wp-par 1 -wp-msg-key shell  -wp-cache update -wp-session=%{read:@WP_CACHE@}
 MACRO: PRINT -then-last -print
 
 MACRO: EVA_PLUGINS eva,scope,inout variadic