#858 improve coverage

Author: martinjrobins

pybamm/models/base_model.py

@@ -381,11 +381,11 @@ def check_well_posedness(self, post_discretisation=False):
         post_discretisation : boolean
             A flag indicating tests to be skipped after discretisation
         """
+        self.check_for_time_derivatives()
         self.check_well_determined(post_discretisation)
         self.check_algebraic_equations(post_discretisation)
         self.check_ics_bcs()
         self.check_default_variables_dictionaries()
-        self.check_for_time_derivatives()
         # Can't check variables after discretising, since Variable objects get replaced
         # by StateVector objects
         # Checking variables is slow, so only do it in debug mode

tests/unit/test_models/test_base_model.py

@@ -248,6 +248,61 @@ def test_check_well_posedness_variables(self):
         ):
             model.check_well_posedness(post_discretisation=True)
 
+        # model must be in semi-explicit form
+        model = pybamm.BaseModel()
+        model.rhs = {c: d.diff(pybamm.t), d: -1}
+        model.initial_conditions = {c: 1, d: 1}
+        with self.assertRaisesRegex(
+            pybamm.ModelError,
+            "time derivative of variable found",
+        ):
+            model.check_well_posedness()
+
+        # model must be in semi-explicit form
+        model = pybamm.BaseModel()
+        model.algebraic = {
+            c: 2 * d - c,
+            d: c * d.diff(pybamm.t) - d,
+        }
+        model.initial_conditions = {c: 1, d: 1}
+        with self.assertRaisesRegex(
+            pybamm.ModelError,
+            "time derivative of variable found",
+        ):
+            model.check_well_posedness()
+
+        # model must be in semi-explicit form
+        model = pybamm.BaseModel()
+        model.rhs = {c: d.diff(pybamm.t), d: -1}
+        model.initial_conditions = {c: 1, d: 1}
+        with self.assertRaisesRegex(
+            pybamm.ModelError,
+            "time derivative of variable found",
+        ):
+            model.check_well_posedness()
+
+        # model must be in semi-explicit form
+        model = pybamm.BaseModel()
+        model.algebraic = {
+            d: 5 * pybamm.StateVector(slice(0, 15)) - 1,
+            c: 5 * pybamm.StateVectorDot(slice(0, 15)) - 1
+        }
+        with self.assertRaisesRegex(
+            pybamm.ModelError,
+            "time derivative of state vector found",
+        ):
+            model.check_well_posedness(post_discretisation=True)
+
+        # model must be in semi-explicit form
+        model = pybamm.BaseModel()
+        model.rhs = {c: 5 * pybamm.StateVectorDot(slice(0, 15)) - 1}
+        model.initial_conditions = {c: 1}
+        with self.assertRaisesRegex(
+            pybamm.ModelError,
+            "time derivative of state vector found",
+        ):
+            model.check_well_posedness(post_discretisation=True)
+
     def test_check_well_posedness_initial_boundary_conditions(self):
         # Well-posed model - Dirichlet
         whole_cell = ["negative electrode", "separator", "positive electrode"]