Tests checking implementation of checkpointing/SolverState (#173)

* Add tests to check if SolverState stores and returns the checkpointed state correctly

---------

Co-authored-by: Benjamin Rodenberg <[email protected]>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # FEniCS-preCICE adapter changelog
 
+## latest
+
+* Add unit tests for checkpointing. [#173](https://github.com/precice/fenics-adapter/pull/173)
+
 ## 2.1.0
 
 * Additionally support checkpoints being provided as a list or tuple (of FEniCS Functions). [#170](https://github.com/precice/fenics-adapter/pull/170)

tests/unit/test_checkpointing.py

@@ -0,0 +1,97 @@
+from unittest.mock import MagicMock
+from unittest import TestCase
+from fenics import FunctionSpace, UnitSquareMesh, Expression, interpolate
+from fenicsprecice.solverstate import SolverState
+
+
+class TestCheckpointing(TestCase):
+    def test_solverstate_basic(self):
+        """
+        Check if correct values are read from the checkpoint, while the state of the object that is copied is not changed
+        """
+        n = 1
+        size = 5
+        mesh = UnitSquareMesh(size,size)
+        V = FunctionSpace(mesh, 'P', 2)
+        dummy_value = 1
+        E = Expression("t", t=dummy_value, degree=2)
+        u = interpolate(E, V)
+
+        # "write checkpoint"
+        sstate = SolverState(u, dummy_value, n)
+        # "read checkpoint"
+        u_cp, t_cp, n_cp = sstate.get_state()
+
+        #check values
+        self.assertEqual(t_cp, dummy_value)
+        self.assertEqual(n, n_cp)
+        #function should be the same everywhere (-> check vector values of the function)
+        vec_u = u.vector()
+        vec_u_cp = u_cp.vector()
+        for i in range(size*size):
+            self.assertAlmostEqual(vec_u[i], vec_u_cp[i])
+
+    def test_solverstate_modification_vector(self):
+        """
+        Check if correct values are read from the checkpoint, if the dof vector of the dolfin functions are changed directly 
+
+        Motivation for this test: Related to https://github.com/precice/fenics-adapter/pull/172 and https://github.com/precice/tutorials/pull/554
+        """
+        n = 1
+        size = 5
+        mesh = UnitSquareMesh(size,size)
+        V = FunctionSpace(mesh, 'P', 2)
+        ref_value = 1
+        E = Expression("t", t=ref_value, degree=2)
+        u = interpolate(E, V)
+
+        # "write checkpoint"
+        sstate = SolverState(u, ref_value, n)
+
+        # modify state of u
+        dummy_value = ref_value + 2
+        u.vector()[:] = dummy_value
+
+        # "read checkpoint"
+        u_cp, _, _ = sstate.get_state()
+
+        #check values
+        #function should be the same everywhere
+        #(so the vector values should all be ref_value)
+        vec_u_cp = u_cp.vector()
+        for i in range(size*size):
+            self.assertAlmostEqual(ref_value, vec_u_cp[i])
+
+
+    def test_solverstate_modification_assign(self):
+        """
+        Check if correct values are read from the checkpoint, if the dof of the dolfin functions are changed with the assign function
+        and not directly via the dof vector
+        """
+        n = 1
+        size = 5
+        mesh = UnitSquareMesh(size,size)
+        V = FunctionSpace(mesh, 'P', 2)
+        ref_value = 1
+        E = Expression("t", t=ref_value, degree=2)
+        u = interpolate(E, V)
+
+        # "write checkpoint"
+        sstate = SolverState(u, ref_value, n)
+
+        # modify state of u
+        # "compute" new solution
+        dummy_value = ref_value + 2
+        E.t = dummy_value
+        u2 = interpolate(E,V)
+        u.assign(u2)
+
+        # "read checkpoint"
+        u_cp, _, _ = sstate.get_state()
+
+        #check values
+        #function should be the same everywhere
+        #(so the vector values should all be ref_value)
+        vec_u_cp = u_cp.vector()
+        for i in range(size*size):
+            self.assertAlmostEqual(ref_value, vec_u_cp[i])