test(melange): add a test that introduces rules in the target dir

Signed-off-by: Antonio Nuno Monteiro <[email protected]>

test/blackbox-tests/test-cases/melange/add-rules-under-melange-emit-target.t

@@ -0,0 +1,48 @@
+Test that the target directory exists
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.7)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (alias melange)
+  >  (target output)
+  >  (module_system commonjs))
+  > EOF
+
+Create the target dir
+
+  $ mkdir ./output
+  $ cat > output/dune <<EOF
+  > (rule
+  >  (with-stdout-to index.txt (echo "hello")))
+  > (alias (name melange) (deps index.txt))
+  > EOF
+  $ cat > hello.ml <<EOF
+  > let () = Js.log "hello"
+  > EOF
+
+  $ dune build @melange
+  $ ls _build/default/output
+  hello.js
+  index.txt
+
+Target promotion works
+
+  $ dune clean
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (alias melange)
+  >  (target output)
+  >  (promote (until-clean))
+  >  (module_system commonjs))
+  > EOF
+
+  $ dune build @melange
+  $ ls _build/default/output
+  hello.js
+  index.txt
+
+