test(melange): show (melange.emit ..) doesn't respect -p <PKG> (#13521)

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

Author: anmonteiro

test/blackbox-tests/test-cases/melange/melange-runtest-multiple-packages.t

@@ -0,0 +1,41 @@
+Show interaction of `dune runtest -p ..` and `(melange.emit ..)`
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.22)
+  > (using melange 1.0)
+  > (package (name a))
+  > (package (name b))
+  > EOF
+
+  $ mkdir a b
+  $ cat > a/dune <<EOF
+  > (melange.emit
+  >  (alias runtest)
+  >  (package a)
+  >  (emit_stdlib false)
+  >  (target out))
+  > EOF
+  $ cat > a/x.ml <<EOF
+  > let () = print_endline "hello"
+  > EOF
+
+  $ cat > b/dune <<EOF
+  > (melange.emit
+  >  (alias runtest)
+  >  (package b)
+  >  (emit_stdlib false)
+  >  (target out))
+  > EOF
+  $ cat > b/x.ml <<EOF
+  > let () = print_endline "hello"
+  > EOF
+
+Selecting only the package a should not build b
+
+  $ dune runtest -p a
+  $ ls _build/default/b/out/b
+  x.js
+
+  $ dune runtest -p b
+  $ ls _build/default/b/out/b
+  x.js