Update tests

Signed-off-by: Nicolás Ojeda Bär <[email protected]>

test/blackbox-tests/test-cases/copy_files.t/run.t

@@ -44,3 +44,34 @@ Test (alias ...) and (mode ...) fields:
 
   $ cat test3/foo.txt
   Foo
+
+Test external paths:
+
+  $ mkdir -p test4
+  $ cat >test4/dune-project <<EOF
+  > (lang dune 2.6)
+  > EOF
+  $ echo Hola > foo.txt
+  $ P=$(pwd)/foo.txt
+  $ echo $P
+  $TESTCASE_ROOT/foo.txt
+  $ cat >test4/dune <<EOF
+  > (copy_files $P)
+  > EOF
+  $ dune build --root test4 foo.txt
+  Entering directory 'test4'
+  File "dune", line 1, characters 12-105:
+  1 | (copy_files $TESTCASE_ROOT/foo.txt)
+                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  Error:
+  $TESTCASE_ROOT/foo.txt
+  is an absolute path. This is only available since version 2.7 of the dune
+  language. Please update your dune-project file to have (lang dune 2.7).
+  [1]
+  $ cat >test4/dune-project <<EOF
+  > (lang dune 2.7)
+  > EOF
+  $ dune build --root test4 foo.txt
+  Entering directory 'test4'
+  $ cat test4/_build/default/foo.txt
+  Hola