#858 fix coverage and flake8

pybamm/expression_tree/state_vector.py

@@ -242,15 +242,13 @@ def _base_evaluate(self, t=None, y=None, y_dot=None, u=None):
         return out
 
     def diff(self, variable):
-        if variable.id == self.id:
-            return pybamm.Scalar(1)
-        elif variable.id == pybamm.t.id:
+        if variable.id == pybamm.t.id:
             return StateVectorDot(*self._y_slices, name=self.name + "'",
                                   domain=self.domain,
                                   auxiliary_domains=self.auxiliary_domains,
                                   evaluation_array=self.evaluation_array)
         else:
-            return pybamm.Scalar(0)
+            raise NotImplementedError
 
     def _jac(self, variable):
         if isinstance(variable, pybamm.StateVector):
@@ -309,14 +307,12 @@ def _base_evaluate(self, t=None, y=None, y_dot=None, u=None):
         return out
 
     def diff(self, variable):
-        if variable.id == self.id:
-            return pybamm.Scalar(1)
-        elif variable.id == pybamm.t.id:
+        if variable.id == pybamm.t.id:
             raise pybamm.ModelError(
                 "cannot take second time derivative of a state vector"
             )
         else:
-            return pybamm.Scalar(0)
+            raise NotImplementedError
 
     def _jac(self, variable):
         if isinstance(variable, pybamm.StateVectorDot):

tests/unit/test_discretisations/test_discretisation.py

@@ -703,7 +703,8 @@ def test_process_model_ode(self):
         # test that any time derivatives of variables in rhs raises an
         # error
         model = pybamm.BaseModel()
-        model.rhs = {c: pybamm.div(N) + c.diff(pybamm.t), T: pybamm.div(q), S: pybamm.div(p)}
+        model.rhs = {c: pybamm.div(N) + c.diff(pybamm.t),
+                     T: pybamm.div(q), S: pybamm.div(p)}
         model.initial_conditions = {
             c: pybamm.Scalar(2),
             T: pybamm.Scalar(5),
@@ -846,8 +847,6 @@ def test_process_model_dae(self):
         with self.assertRaises(pybamm.ModelError):
             disc.process_model(model)
 
-
-
     def test_process_model_concatenation(self):
         # concatenation of variables as the key
         cn = pybamm.Variable("c", domain=["negative electrode"])
@@ -1144,6 +1143,7 @@ def test_mass_matirx_inverse(self):
             model.mass_matrix_inv.entries.toarray(), mass_inv.toarray()
         )
 
+
 if __name__ == "__main__":
     print("Add -v for more debug output")
     import sys

tests/unit/test_expression_tree/test_d_dt.py

@@ -22,8 +22,8 @@ def test_time_derivative(self):
         self.assertEqual(a.simplify().id, (2 * pybamm.t).id)
         self.assertEqual(a.evaluate(t=1), 2)
 
-        a =(2 + pybamm.t**2).diff(pybamm.t)
-        self.assertEqual(a.simplify().id, (2*pybamm.t).id)
+        a = (2 + pybamm.t**2).diff(pybamm.t)
+        self.assertEqual(a.simplify().id, (2 * pybamm.t).id)
         self.assertEqual(a.evaluate(t=1), 2)
 
     def test_time_derivative_of_variable(self):
@@ -33,7 +33,7 @@ def test_time_derivative_of_variable(self):
         self.assertEqual(a.name, "a'")
 
         p = pybamm.Parameter('p')
-        a = (1 + p*pybamm.Variable('a')).diff(pybamm.t).simplify()
+        a = (1 + p * pybamm.Variable('a')).diff(pybamm.t).simplify()
         self.assertIsInstance(a, pybamm.Multiplication)
         self.assertEqual(a.children[0].name, 'p')
         self.assertEqual(a.children[1].name, "a'")
@@ -59,6 +59,7 @@ def test_time_derivative_of_state_vector(self):
         with self.assertRaises(pybamm.ModelError):
             a = (sv).diff(pybamm.t).diff(pybamm.t)
 
+
 if __name__ == "__main__":
     print("Add -v for more debug output")
     import sys

tests/unit/test_expression_tree/test_operations/test_convert_to_casadi.py

@@ -201,7 +201,8 @@ def test_convert_external_variable(self):
 
         # External only
         self.assert_casadi_equal(
-            pybamm_u1.to_casadi(casadi_t, casadi_y, u=casadi_us), casadi_us["External 1"]
+            pybamm_u1.to_casadi(casadi_t, casadi_y, u=casadi_us),
+            casadi_us["External 1"]
         )
 
         # More complex

tests/unit/test_expression_tree/test_state_vector.py

@@ -35,6 +35,14 @@ def test_evaluate_list(self):
         y = np.linspace(0, 3, 31)
         np.testing.assert_array_almost_equal(sv.evaluate(y=y), y[:, np.newaxis])
 
+    def test_diff(self):
+        a = pybamm.StateVector(slice(0, 10))
+        with self.assertRaises(NotImplementedError):
+            a.diff(a)
+        b = pybamm.StateVectorDot(slice(0, 10))
+        with self.assertRaises(NotImplementedError):
+            a.diff(b)
+
     def test_name(self):
         sv = pybamm.StateVector(slice(0, 10))
         self.assertEqual(sv.name, "y[0:10]")
@@ -61,6 +69,7 @@ def test_failure(self):
         with self.assertRaisesRegex(TypeError, "all y_slices must be slice objects"):
             pybamm.StateVector(slice(0, 10), 1)
 
+
 class TestStateVectorDot(unittest.TestCase):
     def test_evaluate(self):
         sv = pybamm.StateVectorDot(slice(0, 10))
@@ -72,14 +81,16 @@ def test_evaluate(self):
         # Try evaluating with a y that is too short
         y_dot2 = np.ones(5)
         with self.assertRaisesRegex(
-            ValueError, "y_dot is too short, so value with slice is smaller than expected"
+            ValueError,
+            "y_dot is too short, so value with slice is smaller than expected"
         ):
             sv.evaluate(y_dot=y_dot2)
 
     def test_name(self):
         sv = pybamm.StateVectorDot(slice(0, 10))
         self.assertEqual(sv.name, "y_dot[0:10]")
 
+
 if __name__ == "__main__":
     print("Add -v for more debug output")
     import sys

tests/unit/test_parameters/test_parameters_cli.py

@@ -120,6 +120,7 @@ def test_list_params(self):
         # but must not intefere with existing input dir if it exists
         # in the current dir...
 
+
 if __name__ == "__main__":
     print("Add -v for more debug output")
     import sys