Add MiniZinc model verification in tests

Introduce mzn verification utilities and integrate MiniZinc validation into unit tests. Added tests/mzn_verifier.py with verify_mzn_text and assert_valid_mzn helpers (refactoring CLI invocation to a single model-check call and returning (ok, message)). Updated tests/conftest.py to auto-verify rendered models when the MiniZinc CLI is available (monkeypatches Model._render_model_string to collect outputs and fail tests on invalid models); skips verification when minizinc is not found to keep local workflows fast. Updated several tests to call assert_valid_mzn and added a new expression embedding render test to ensure generated MiniZinc is valid.

Author: Arthod

tests/conftest.py

@@ -1,4 +1,7 @@
 import pytest
+import shutil
+
+from tests.mzn_verifier import verify_mzn_text
 
 
 def _has_minizinc_runtime() -> bool:
@@ -18,3 +21,34 @@ def pytest_collection_modifyitems(config, items):
     for item in items:
         if ("integration" in item.keywords):
             item.add_marker(skip_integration)
+
+
+@pytest.fixture(autouse=True)
+def verify_rendered_mzn_models(monkeypatch):
+    # Keep local/unit workflow fast when CLI is unavailable.
+    if (shutil.which("minizinc") is None):
+        yield
+        return
+
+    import pymzm
+
+    original_render = pymzm.Model._render_model_string
+    rendered_models = []
+
+    def _wrapped_render(self, *args, **kwargs):
+        rendered = original_render(self, *args, **kwargs)
+        rendered_models.append(rendered)
+        return rendered
+
+    monkeypatch.setattr(pymzm.Model, "_render_model_string", _wrapped_render)
+    yield
+
+    seen = set()
+    for rendered in rendered_models:
+        if (rendered in seen):
+            continue
+        seen.add(rendered)
+
+        ok, message = verify_mzn_text(rendered)
+        if (not ok):
+            pytest.fail(f"Generated invalid MiniZinc model:\n{message}\n\nModel:\n{rendered}")

tests/mzn_verifier.py

@@ -13,39 +13,27 @@ def _verify_with_minizinc_cli(model_path: Path):
     if (cli is None):
         return False, "MiniZinc CLI not found"
 
-    # Prefer explicit model-check mode and fall back to legacy spellings when unavailable.
-    candidate_args = [
-        ["--model-check-only", str(model_path)],
-        ["--check-only", str(model_path)],
-    ]
-
-    last_error = ""
-    for args in candidate_args:
-        proc = subprocess.run(
-            [cli, *args],
-            stdout=subprocess.PIPE,
-            stderr=subprocess.PIPE,
-            text=True,
-        )
-        if (proc.returncode == 0):
-            return True, ""
-
-        stderr = (proc.stderr or "").strip().lower()
-        if ("unknown option" in stderr or "unrecognized option" in stderr):
-            last_error = proc.stderr or proc.stdout
-            continue
-
-        return False, (proc.stderr or proc.stdout or "MiniZinc verification failed")
-
-    return False, (last_error or "MiniZinc verification failed")
-
-
-def assert_valid_mzn_or_skip(testcase, mzn_text: str):
+    proc = subprocess.run(
+        [cli, "--model-check-only", str(model_path)],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+    )
+    if (proc.returncode == 0):
+        return True, ""
+
+    return False, (proc.stderr or proc.stdout or "MiniZinc verification failed")
+
+
+def verify_mzn_text(mzn_text: str):
     with tempfile.TemporaryDirectory() as tmpdir:
         model_path = Path(tmpdir) / "model.mzn"
         model_path.write_text(mzn_text, encoding="utf-8")
+        return _verify_with_minizinc_cli(model_path)
+
 
-        ok, message = _verify_with_minizinc_cli(model_path)
-        if (not ok and "cli not found" in message.lower()):
-            testcase.skipTest(message)
-        testcase.assertTrue(ok, msg=message)
+def assert_valid_mzn(testcase, mzn_text: str):
+    ok, message = verify_mzn_text(mzn_text)
+    if (not ok and "cli not found" in message.lower()):
+        testcase.skipTest(message)
+    testcase.assertTrue(ok, msg=message)

tests/test_architecture.py

@@ -4,6 +4,7 @@
 import pymzm
 
 from pymzm.backends import MznTextBackend
+from tests.mzn_verifier import assert_valid_mzn
 
 
 pytestmark = [pytest.mark.unit]
@@ -27,6 +28,7 @@ def test_model_to_ir_and_backend_render(self):
         expected = MznTextBackend().render_model(model_ir)
         model.generate()
         self.assertEqual(model.model_mzn_str, expected)
+        assert_valid_mzn(self, model.model_mzn_str)
 
 
 if __name__ == "__main__":

tests/test_deterministic_generation.py

@@ -2,6 +2,7 @@
 import pytest
 
 import pymzm
+from tests.mzn_verifier import assert_valid_mzn
 
 
 pytestmark = [pytest.mark.unit, pytest.mark.snapshot]
@@ -54,6 +55,7 @@ def test_generate_is_deterministic_for_symbols_and_includes(self):
         self.assertIn('int: b = 2;', lines)
         self.assertLess(lines.index('int: a = 1;'), lines.index('int: b = 2;'))
         self.assertLess(lines.index('var 1..3: x;'), lines.index('var 1..3: y;'))
+        assert_valid_mzn(self, model_a.model_mzn_str)
 
 
 if __name__ == "__main__":

tests/test_expression_validation.py

@@ -2,6 +2,7 @@
 import pytest
 
 import pymzm
+from tests.mzn_verifier import assert_valid_mzn
 
 
 pytestmark = [pytest.mark.unit]
@@ -111,6 +112,22 @@ def test_conditional_validates_branches_and_else(self):
         self.assertRaises(pymzm.PymzmValueIsNotExpression, pymzm.Expression.conditional, [(x >= 1, object())], 0)
         self.assertRaises(pymzm.PymzmValueIsNotExpression, pymzm.Expression.conditional, [(x >= 1, 1)], object())
 
+    def test_expression_render_is_valid_mzn_when_embedded_in_model(self):
+        model = pymzm.Model()
+        x = model.add_variable("x", val_min=0, val_max=10)
+
+        y_expr = pymzm.Expression.let(["int: y = x + 1"], pymzm.Expression("y"))
+        guard = pymzm.Expression.conditional([(x >= 5, True), (x >= 2, x >= 3)], False)
+        q = pymzm.Expression.forall("i", range(1, 4), lambda i: x >= i)
+
+        model.add_constraint(guard)
+        model.add_constraint(q)
+        model.add_constraint(y_expr >= 1)
+        model.set_solve_criteria(pymzm.SOLVE_MAXIMIZE, y_expr)
+        model.generate()
+
+        assert_valid_mzn(self, model.model_mzn_str)
+
 
 if __name__ == "__main__":
     unittest.main()