test: depopts with constraints (ocaml#9434)

Signed-off-by: Ali Caglayan <alizter@gmail.com>

test/blackbox-tests/test-cases/pkg/depopts/depopts-with-constraints.t

@@ -0,0 +1,39 @@
+We test how the solver chooses a solution for depopts with constraints.
+
+  $ . ../helpers.sh
+  $ mkrepo
+
+We create a package "foo" that is the dependency of two packages "optional" and
+"bar".
+
+  $ mkpkg foo 1
+
+The package "optional" has a constraint on a particular version of "foo". 
+
+  $ mkpkg optional <<'EOF'
+  > depends: [ "foo" {= "1"} ]
+  > EOF
+
+The package "bar" depends on "foo" and depends optionally on "optional".
+
+  $ mkpkg bar <<'EOF'
+  > depends: [ "foo" ]
+  > depopts: [ "optional" ]
+  > EOF
+
+Here the solver could pick "bar" and "foo", and perphaps pick "optional",
+however this is not required.
+
+  $ solve bar
+  Solution for dune.lock:
+  - bar.0.0.1
+  - foo.1
+
+Since the version of "foo" is constrained by "optional", "optional" should be
+excluded from the build plan if the latest version of "foo" is picked.
+
+  $ mkpkg foo 2
+  $ solve bar
+  Solution for dune.lock:
+  - bar.0.0.1
+  - foo.2