add test for sequential solve

Author: hitonanode

test/test_sequential_solve.py

@@ -0,0 +1,50 @@
+from typing import cast
+
+import pytest
+
+from lpmodeler.model import LPModel, LPStatus, LPVar
+
+
+def test_sequential_solve() -> None:
+    x = LPVar("x", lower_bound=0)
+
+    model = LPModel()
+
+    model.set_objective(x)
+
+    model.solve()
+
+    assert model.status == LPStatus.OPTIMAL
+    assert x.value() == pytest.approx(0.0)
+    assert model.objective.value() == pytest.approx(0.0)
+
+    model.add_constraint(x >= 1)
+
+    model.solve()
+
+    assert model.status == LPStatus.OPTIMAL
+    assert x.value() == pytest.approx(1.0)
+    assert model.objective.value() == pytest.approx(1.0)
+
+
+def test_sequential_solve_no_solution() -> None:
+    x = LPVar("x", lower_bound=0)
+
+    model = LPModel()
+
+    model.set_objective(x)
+
+    model.solve()
+
+    assert model.status == LPStatus.OPTIMAL
+    assert x.value() == pytest.approx(0.0)
+    assert model.objective.value() == pytest.approx(0.0)
+
+    model.add_constraint(x <= -1)
+
+    model.solve()
+
+    status2 = cast(LPStatus, model.status)
+    assert status2 == LPStatus.INFEASIBLE
+    assert x.value() is None
+    assert model.objective.value() is None