Clarify why test case ordering is necessary

and delete comment in code about static variables that can no longer be
reproduced.

python/test/test_basic.py

@@ -7,56 +7,22 @@ from .pytest_common import pushd
 class TestBasic(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
-        # NOTE: Loading the below extension module involves loading a
-        #    a shared library like "simulators.cpython-37m-x86_64-linux-gnu.so"
-        #    It turns out Python cannot unload this module, see:
-        #
-        #  https://stackoverflow.com/a/8295590/2173773
-        #  https://bugs.python.org/issue34309
-        #
-        #    This is a problem when we want to create a new instance for each unit
-        #    test. For example, when creating the first instance, static variables in
-        #    in the shared object are initialized. However, when the
-        #    corresponding Python object is later deleted (when the test finishes),
-        #    the shared object is not unloaded and its static variables
-        #    stays the same. So when a second Python instance is created,
-        #    the same address is used for the static variables in the shared library
-        #    i.e. the static variables are referring to the same memory location
-        #    as for the first object (and they are not reinitialized).
-        #
-        #    Unfortunatly, this leads to undefined behavior since the C++ code
-        #    for flow simulation uses static variable to keep state information
-        #    and since it was not built under the assumption that it would
-        #    used as a shared library. It was assumed (?) that a flow simulation
-        #    was executed from an executable file (not library file) and only
-        #    executed once. To execute another simulation, it was assumed that
-        #    the executable would be restarted from a controlling program like
-        #    the Shell (which would reload and initialize the object into fresh memory).
-        #
-        #  TODO: Fix the C++ code such that it allows multiple runs whith the same
-        #     object file.
-        #
-        #  NOTE:  The result of the above is that we can only instantiate a
-        #    single simulator object during the unit tests.
-        #    This is not how the unittest module was supposed to be used. Usually one
-        #    would write multiple test_xxx() methods that are independent and
-        #    each method receives a new simulator object (also note that the order
-        #    in which each test_xxx() method is called by unittest is not defined).
-        #    However, as noted above this is not currently possible.
-        #
         test_dir = Path(os.path.dirname(__file__))
         cls.data_dir_bo = test_dir.parent.joinpath("test_data/SPE1CASE1a")
         cls.data_dir_gw = test_dir.parent.joinpath("test_data/SPE1CASE2")
 
+    # IMPORTANT: Since all the python unittests run in the same process we must be
+    #  careful to not call MPI_Init() more than once.
+    #  Tests are run alphabetically, so we need to make sure that
+    #  the the first test calls MPI_Init(), therefore the name of the tests
+    #  have a numeric label like "01" in test_01_blackoil to ensure that they
+    #  are run in a given order.
 
-    def test_all(self):
-        self._bo()
-        self._gw()
-
-    def _bo(self):
+    # IMPORTANT: This test must be run first since it calls MPI_Init()
+    def test_01_blackoil(self):
         with pushd(self.data_dir_bo):
             sim = BlackOilSimulator(args=['--linear-solver=ilu0'], filename="SPE1CASE1.DATA")
-            sim.setup_mpi(True, False)
+            sim.setup_mpi(init=True, finalize=False)
             sim.step_init()
             sim.step()
             dt = sim.get_dt()
@@ -79,10 +45,11 @@ class TestBasic(unittest.TestCase):
             poro2 = sim.get_porosity()
             self.assertAlmostEqual(poro2[0], 0.285, places=7, msg='value of porosity 2')
 
-    def _gw(self):
+    # IMPORTANT: This test must be run last since it calls MPI_Finalize()
+    def test_99_gaswater(self):
         with pushd(self.data_dir_gw):
             sim = GasWaterSimulator(args=['--linear-solver=ilu0'], filename="SPE1CASE2_GASWATER.DATA")
-            sim.setup_mpi(False, True)
+            sim.setup_mpi(init=False, finalize=True)
             sim.step_init()
             sim.step()
             dt = sim.get_dt()  # 31 days = 31 * 24 * 60 * 60 = 2678400 seconds

python/test/test_fluidstate_variables.py

@@ -7,19 +7,19 @@ from .pytest_common import pushd
 class TestBasic(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
-        # NOTE: See comment in test_basic.py for the reason why we are
-        #   only using a single test_all() function instead of splitting
-        #   it up in multiple test functions
         test_dir = Path(os.path.dirname(__file__))
         cls.data_dir_bo = test_dir.parent.joinpath("test_data/SPE1CASE1a")
         cls.data_dir_gw = test_dir.parent.joinpath("test_data/SPE1CASE2")
 
+    # IMPORTANT: Since all the python unittests run in the same process we must be
+    #  careful to not call MPI_Init() more than once.
+    #  Tests are run alphabetically, so we need to make sure that
+    #  the the first test calls MPI_Init(), therefore the name of the tests
+    #  have a numeric label like "01" in test_01_bo to ensure that they
+    #  are run in a given order.
 
-    def test_all(self):
-        self._bo()
-        self._gw()
-
-    def _bo(self):
+    # IMPORTANT:This test must be run first since it calls MPI_Init()
+    def test_01_blackoil(self):
         with pushd(self.data_dir_bo):
             sim = BlackOilSimulator("SPE1CASE1.DATA")
             sim.setup_mpi(True, False)
@@ -50,7 +50,8 @@ class TestBasic(unittest.TestCase):
             T = sim.get_fluidstate_variable(name='T')
             self.assertAlmostEqual(T[0], 288.705, places=3, msg='value of temperature')
 
-    def _gw(self):
+    # IMPORTANT: This test must be run last since it calls MPI_Finalize()
+    def test_99_gaswater(self):
         with pushd(self.data_dir_gw):
             sim = GasWaterSimulator("SPE1CASE2_GASWATER.DATA")
             sim.setup_mpi(False, True)
@@ -67,4 +68,4 @@ class TestBasic(unittest.TestCase):
             Sg = sim.get_fluidstate_variable(name='Sg')
             self.assertAlmostEqual(Sg[0], 0.708648, places=3, msg='value of gas saturation')
             Sw = sim.get_fluidstate_variable(name='Sw')
-            self.assertAlmostEqual(Sw[0], 0.291351, places=5, msg='value of water saturation')
+            self.assertAlmostEqual(Sw[0], 0.291351, places=5, msg='value of water saturation')

python/test/test_mpi.py

@@ -7,13 +7,12 @@ from .pytest_common import pushd
 class TestBasic(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
-        # NOTE: See comment in test_basic.py for the reason why we are
-        #   only using a single test_all() function instead of splitting
-        #   it up in multiple test functions
         test_dir = Path(os.path.dirname(__file__))
         cls.data_dir = test_dir.parent.joinpath("test_data/SPE1CASE1a")
 
-    # IMPORTANT: Tests are run alphabetically, so we need to make sure that
+    # IMPORTANT: Since all the python unittests run in the same process we must be
+    #  careful to not call MPI_Init() more than once.
+    #  Tests are run alphabetically, so we need to make sure that
     #  the the first test calls MPI_Init(), therefore the name of the tests
     #  have a numeric label like "01" in test_01_mpi_init to ensure that they
     #  are run in a given order.