test(pkg): show precedence of make and gmake (#8750)

Signed-off-by: Ali Caglayan <[email protected]>

test/blackbox-tests/test-cases/pkg/opam-var/make-over-gmake.t

@@ -0,0 +1,24 @@
+  $ . ./opam-var-helpers.sh 
+
+If both make and gmake are available, we should prefer make.
+
+opam doesn't resolve make but rather runs make literally so it is up to whatever is in
+PATH to resolve it. This does mean that make is preferred over gmake so we should
+replicate that behaviour.
+
+We create a dummy package that will output the value of the opam make variable:
+  $ mkrepo
+  > mkpkg testpkg << EOF
+  > opam-version: "2.0"
+  > build: [ "echo" make ]
+  > EOF
+  > solve testpkg 2> /dev/null
+
+We now create dummy versions of make and gmake.
+  $ cat > make; cat > gmake
+We add the current directory to PATH. Dune will expand %{make} and should prefer make over
+gmake.
+  $ PATH=.:$PATH
+  > build_pkg testpkg
+  $TESTCASE_ROOT/gmake
+