Add tests for tranquilo version check error handling

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: timmens

tests/optimagic/optimizers/test_tranquilo.py

@@ -0,0 +1,50 @@
+import numpy as np
+import pytest
+
+from optimagic.exceptions import NotInstalledError
+from optimagic.optimizers.tranquilo import Tranquilo, TranquiloLS
+
+
+@pytest.fixture()
+def mock_problem():
+    """Create a minimal mock of InternalOptimizationProblem."""
+
+    class MockBounds:
+        lower = np.array([-1.0, -1.0])
+        upper = np.array([1.0, 1.0])
+
+    class MockProblem:
+        bounds = MockBounds()
+
+        def batch_fun(self, xs):
+            return [np.sum(x**2) for x in xs]
+
+    return MockProblem()
+
+
+def test_tranquilo_raises_if_version_too_old(monkeypatch, mock_problem):
+    import optimagic.optimizers.tranquilo as tranquilo_mod
+
+    monkeypatch.setattr(
+        tranquilo_mod, "IS_TRANQUILO_VERSION_NEWER_OR_EQUAL_TO_0_1_0", False
+    )
+
+    algo = Tranquilo()
+    x0 = np.array([0.5, 0.5])
+
+    with pytest.raises(NotInstalledError, match="tranquilo"):
+        algo._solve_internal_problem(mock_problem, x0)
+
+
+def test_tranquilo_ls_raises_if_version_too_old(monkeypatch, mock_problem):
+    import optimagic.optimizers.tranquilo as tranquilo_mod
+
+    monkeypatch.setattr(
+        tranquilo_mod, "IS_TRANQUILO_VERSION_NEWER_OR_EQUAL_TO_0_1_0", False
+    )
+
+    algo = TranquiloLS()
+    x0 = np.array([0.5, 0.5])
+
+    with pytest.raises(NotInstalledError, match="tranquilo"):
+        algo._solve_internal_problem(mock_problem, x0)