Mark a few more tests as slow (#1292)

Some of the tests are extremely time-consuming on even a fast parallel
Linux VM. Two of tests marked in this commit clocked in at **20 minutes
each** even when running with `-n 30`. The following numbers are from
using the pytest `--durations` option:

* 1288.49s call
src/openfermion/ops/representations/doci_hamiltonian_test.py::IntegralTransformsTest::test_fermionic_hamiltonian_from_integrals

* 1208.20s call
src/openfermion/transforms/opconversions/remove_symmetry_qubits_test.py::ReduceSymmetryQubitsTest::test_energy_reduce_symmetry_qubits

Two other tests were in the 600-700 sec range, and they are marked as
slow in this PR as well. The use of `@pytest.mark.slow` allows the user
to run pytest with `-m "not slow"` to skip the these tests and some
other tests in OpenFermion that are already marked as slow.

Note: the changes to the imports are purely formatting/linting changes
brought about by running check/format-incremental.

Author: mhucka

src/openfermion/ops/representations/doci_hamiltonian_test.py

@@ -16,6 +16,7 @@
 import unittest
 
 import numpy
+import pytest
 
 from openfermion.config import EQ_TOLERANCE
 from openfermion.chem.molecular_data import MolecularData
@@ -24,11 +25,9 @@
 from openfermion.linalg import get_sparse_operator
 from openfermion.ops.representations.doci_hamiltonian import (
     DOCIHamiltonian,
-    get_tensors_from_doci,
-    get_projected_integrals_from_doci,
     get_doci_from_integrals,
 )
-from openfermion import get_fermion_operator, InteractionOperator, normal_ordered
+from openfermion import get_fermion_operator, InteractionOperator
 
 numpy.set_printoptions(linewidth=2000, threshold=sys.maxsize)
 
@@ -55,6 +54,7 @@ def test_integrals_self_inverse(self):
         self.assertTrue(numpy.allclose(hr1, hr1_test))
         self.assertTrue(numpy.allclose(hr2, hr2_test))
 
+    @pytest.mark.slow
     def test_fermionic_hamiltonian_from_integrals(self):
         constant = self.molecule.nuclear_repulsion
         doci_constant = constant

src/openfermion/resource_estimates/pbc/thc/factorizations/isdf_test.py

@@ -10,6 +10,7 @@
 #   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
+
 import numpy as np
 import pytest
 
@@ -253,6 +254,7 @@ def test_G_vector_mapping_single_translation():
 
 
 @pytest.mark.skipif(not HAVE_DEPS_FOR_RESOURCE_ESTIMATES, reason='pyscf and/or jax not installed.')
+@pytest.mark.slow
 def test_kpoint_isdf_double_translation():
     cell = gto.Cell()
     cell.atom = """
@@ -300,6 +302,7 @@ def test_kpoint_isdf_double_translation():
 
 
 @pytest.mark.skipif(not HAVE_DEPS_FOR_RESOURCE_ESTIMATES, reason='pyscf and/or jax not installed.')
+@pytest.mark.slow
 def test_kpoint_isdf_single_translation():
     cell = gto.Cell()
     cell.atom = """

src/openfermion/transforms/opconversions/remove_symmetry_qubits_test.py

@@ -16,6 +16,8 @@
 
 import unittest
 
+import pytest
+
 from openfermion.hamiltonians import fermi_hubbard
 from openfermion.chem import MolecularData
 from openfermion.transforms.opconversions import get_fermion_operator
@@ -83,6 +85,7 @@ def number_of_qubits(qubit_hamiltonian, unreduced_orbitals):
 class ReduceSymmetryQubitsTest(unittest.TestCase):
     # Check whether fermionic and reduced qubit Hamiltonians
     # have the same energy for LiH
+    @pytest.mark.slow
     def test_energy_reduce_symmetry_qubits(self):
         # Generate the fermionic Hamiltonians,
         # number of orbitals and number of electrons.