Added test showcasing one of the bugs: (#12726)

eager watch mode doesn't register promotions at all for diff rules (but not cram tests)

Signed-off-by: Ambre Austen Suhamy <[email protected]>
Co-authored-by: Shon Feder <[email protected]>

Author: ElectreAAS

test/blackbox-tests/test-cases/watching/eager-promotion.t

@@ -0,0 +1,56 @@
+This test shows that the eager watch server doesn't register promotions at all
+
+  $ . ./helpers.sh
+
+  $ echo '(lang dune 3.20)' > dune-project
+
+  $ cat > dune << EOF
+  > (rule 
+  >  (alias a)
+  >  (action
+  >   (progn
+  >    (write-file a.output "processed A")
+  >    (diff a a.output))))
+  > EOF
+
+  $ echo "raw A" > a
+
+  $ dune build -w &
+  File "a", line 1, characters 0-0:
+  Error: Files _build/default/a and _build/default/a.output differ.
+  Had 1 error, waiting for filesystem changes...
+  File "a", line 1, characters 0-0:
+  Error: Files _build/default/a and _build/default/a.output differ.
+  Had 1 error, waiting for filesystem changes...
+  Warning: Nothing to promote for a.
+  $ dune rpc ping --wait
+  Server appears to be responding normally
+Added safety measure against racy behaviour.
+  $ sleep 1
+
+Now A should be in the promotion database
+  $ dune build @a
+  File "a", line 1, characters 0-0:
+  Error: Files _build/default/a and _build/default/a.output differ.
+  Error: Build failed with 1 error.
+  [1]
+
+This should be raw, as we haven't promoted yet
+  $ cat a
+  raw A
+
+The promotion database should exist!
+  $ find _build/.to-promote
+  find: '_build/.to-promote': No such file or directory
+  [1]
+
+This should be a success
+  $ dune promote a
+  Success
+
+This should be processed
+  $ cat a
+  raw A
+
+  $ dune shutdown
+  $ wait