Mark more tests as slow

Some of the tests are extremely time-consuming on even a fast parallel
Linux VM. The two tests marked in this commit clocked in at **20
minutes** each. 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

Author: mhucka

src/openfermion/ops/representations/doci_hamiltonian_test.py

@@ -11,24 +11,24 @@
 #   limitations under the License.
 """Tests for doci_hamiltonian.py."""
 
-import sys
 import os
+import sys
 import unittest
 
 import numpy
+import pytest
 
-from openfermion.config import EQ_TOLERANCE
+from openfermion import InteractionOperator, get_fermion_operator, normal_ordered
 from openfermion.chem.molecular_data import MolecularData
-from openfermion.config import DATA_DIRECTORY
-from openfermion.transforms import jordan_wigner
+from openfermion.config import DATA_DIRECTORY, EQ_TOLERANCE
 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,
+    get_projected_integrals_from_doci,
+    get_tensors_from_doci,
 )
-from openfermion import get_fermion_operator, InteractionOperator, normal_ordered
+from openfermion.transforms import jordan_wigner
 
 numpy.set_printoptions(linewidth=2000, threshold=sys.maxsize)
 
@@ -55,6 +55,7 @@ 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/transforms/opconversions/remove_symmetry_qubits_test.py

@@ -16,16 +16,17 @@
 
 import unittest
 
-from openfermion.hamiltonians import fermi_hubbard
+import pytest
+
 from openfermion.chem import MolecularData
-from openfermion.transforms.opconversions import get_fermion_operator
+from openfermion.hamiltonians import fermi_hubbard
+from openfermion.linalg import eigenspectrum
 from openfermion.linalg.sparse_tools import (
     get_sparse_operator,
     jw_get_ground_state_at_particle_number,
 )
-from openfermion.linalg import eigenspectrum
 from openfermion.ops.operators import FermionOperator
-
+from openfermion.transforms.opconversions import get_fermion_operator
 from openfermion.transforms.opconversions.remove_symmetry_qubits import (
     symmetry_conserving_bravyi_kitaev,
 )
@@ -83,6 +84,7 @@ 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.