more tests

Signed-off-by: Arseniy Alekseyev <aalekseyev@janestreet.com>

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

@@ -1,7 +1,6 @@
   $ echo '(lang dune 2.0)' > dune-project
   $ echo file-contents > text-file
 
-
 It's OK if there's no correction:
 
   $ cat > dune <<EOF
@@ -30,6 +29,14 @@ and dune correctly complains
   differ.
   [1]
 
+Promotion works fine:
+
+  $ dune promote
+  Promoting _build/default/text-file-corrected to text-file.
+  $ cat text-file
+  corrected-contents-1
+  $ echo file-contents > text-file
+
 When correction is no longer produced, dune no longer complains.
 (relies on stale artifact deletion, it seems)
 
@@ -42,11 +49,33 @@ When correction is no longer produced, dune no longer complains.
   > )
   > EOF
   $ echo new-contents > text-file
-
   $ dune build @correction1
 
+Promotion should work when sandboxing is used:
+
+  $ cat > dune <<EOF
+  > (alias (name correction1)
+  >   (deps)
+  >   (action
+  >     (progn
+  >       (bash "echo another-correction > text-file-corrected")
+  >       (diff? text-file text-file-corrected)))
+  > )
+  > EOF
+
+  $ dune build @correction1 --sandbox copy
+  File "text-file", line 1, characters 0-0:
+  Error: Files
+  _build/.sandbox/150b972ad59fdd3e13294c94880afcfd/default/text-file and
+  _build/.sandbox/150b972ad59fdd3e13294c94880afcfd/default/text-file-corrected
+  differ.
+  [1]
+
+  $ dune promote
+  Skipping promotion of _build/default/text-file-corrected to text-file as the file is missing.
+
 Dependency on the second argument of diff? is *not* automatically added.
-This is fine if we think of it as an intermediate file rather than dep.
+This is fine because we think of it as an intermediate file rather than dep.
 
   $ cat > dune <<EOF
   > (alias (name correction1)
@@ -61,7 +90,7 @@ This is fine if we think of it as an intermediate file rather than dep.
 
   $ dune build @correction1
 
-But dune looks at this file if it exists. This is clearly a bug.
+But dune looks at this file if it exists. This is a bit of a bug.
 One fix is to not look at it, and flag its existence as an error.
 
   $ dune build text-file-corrected
@@ -75,3 +104,29 @@ One fix is to not look at it, and flag its existence as an error.
   Error: Files _build/default/text-file and _build/default/text-file-corrected
   differ.
   [1]
+
+Sandboxing doesn't necessarily help either because dune thinks
+[diff?] is not worth sandboxing.
+
+  $ dune build text-file-corrected
+  $ dune build @correction1 --sandbox copy
+  File "text-file", line 1, characters 0-0:
+  Error: Files _build/default/text-file and _build/default/text-file-corrected
+  differ.
+  [1]
+
+Sandboxing does help if the command producing the
+correction is non-trivial.
+
+  $ cat > dune <<EOF
+  > (alias (name correction1)
+  >   (deps)
+  >   (action
+  >     (progn
+  >       (bash "true")
+  >       (diff? text-file text-file-corrected)))
+  > )
+  > EOF
+
+  $ dune build @correction1 --sandbox copy
+