Convert pubchem_test.py from using unittest to plain pytest

The failures in CI of the tests may be due to the use of the old Pyton
unittest framework. This PR avoids the use of `unittest` in that file.

Author: mhucka

src/openfermion/chem/pubchem_test.py

@@ -12,9 +12,6 @@
 
 """Tests for pubchem.py."""
 
-import unittest
-from unittest.mock import patch
-
 import numpy
 import pytest
 import pubchempy
@@ -79,24 +76,24 @@ def mock_get_compounds(name, searchtype, record_type='2d'):
 
 
 @using_pubchempy
-class OpenFermionPubChemTest(unittest.TestCase):
+class TestOpenFermionPubChem:
 
-    @patch('pubchempy.get_compounds', mock_get_compounds)
-    def test_water(self):
+    def test_water(self, monkeypatch):
+        monkeypatch.setattr(pubchempy, 'get_compounds', mock_get_compounds)
         water_geometry = geometry_from_pubchem('water')
-        self.water_natoms = len(water_geometry)
-        self.water_atoms = [water_atom[0] for water_atom in water_geometry]
-        water_oxygen_index = self.water_atoms.index('O')
+        water_natoms_actual = len(water_geometry)
+        water_atoms = [water_atom[0] for water_atom in water_geometry]
+        water_oxygen_index = water_atoms.index('O')
         water_oxygen = water_geometry.pop(water_oxygen_index)
         water_oxygen_coordinate = numpy.array(water_oxygen[1])
         water_hydrogen1_coordinate = numpy.array(water_geometry[0][1])
         water_hydrogen2_coordinate = numpy.array(water_geometry[1][1])
         water_oxygen_hydrogen1 = water_hydrogen1_coordinate - water_oxygen_coordinate
         water_oxygen_hydrogen2 = water_hydrogen2_coordinate - water_oxygen_coordinate
 
-        self.water_bond_length_1 = numpy.linalg.norm(water_oxygen_hydrogen1)
-        self.water_bond_length_2 = numpy.linalg.norm(water_oxygen_hydrogen2)
-        self.water_bond_angle = numpy.arccos(
+        water_bond_length_1 = numpy.linalg.norm(water_oxygen_hydrogen1)
+        water_bond_length_2 = numpy.linalg.norm(water_oxygen_hydrogen2)
+        water_bond_angle = numpy.arccos(
             numpy.dot(
                 water_oxygen_hydrogen1,
                 water_oxygen_hydrogen2
@@ -108,51 +105,51 @@ def test_water(self):
         )
 
         water_natoms = 3
-        self.assertEqual(water_natoms, self.water_natoms)
+        assert water_natoms == water_natoms_actual
 
-        self.assertAlmostEqual(self.water_bond_length_1, self.water_bond_length_2, places=4)
+        assert water_bond_length_1 == pytest.approx(water_bond_length_2, abs=1e-4)
         water_bond_length_low = 0.9
         water_bond_length_high = 1.1
-        self.assertTrue(water_bond_length_low <= self.water_bond_length_1)
-        self.assertTrue(water_bond_length_high >= self.water_bond_length_1)
+        assert water_bond_length_low <= water_bond_length_1
+        assert water_bond_length_high >= water_bond_length_1
 
         water_bond_angle_low = 100.0 / 360 * 2 * numpy.pi
         water_bond_angle_high = 110.0 / 360 * 2 * numpy.pi
-        self.assertTrue(water_bond_angle_low <= self.water_bond_angle)
-        self.assertTrue(water_bond_angle_high >= self.water_bond_angle)
+        assert water_bond_angle_low <= water_bond_angle
+        assert water_bond_angle_high >= water_bond_angle
 
-    @patch('pubchempy.get_compounds', mock_get_compounds)
-    def test_helium(self):
+    def test_helium(self, monkeypatch):
+        monkeypatch.setattr(pubchempy, 'get_compounds', mock_get_compounds)
         helium_geometry = geometry_from_pubchem('helium')
-        self.helium_natoms = len(helium_geometry)
+        helium_natoms_actual = len(helium_geometry)
 
         helium_natoms = 1
-        self.assertEqual(helium_natoms, self.helium_natoms)
+        assert helium_natoms == helium_natoms_actual
 
-    @patch('pubchempy.get_compounds', mock_get_compounds)
-    def test_none(self):
+    def test_none(self, monkeypatch):
+        monkeypatch.setattr(pubchempy, 'get_compounds', mock_get_compounds)
         none_geometry = geometry_from_pubchem('none')
 
-        self.assertIsNone(none_geometry)
+        assert none_geometry is None
 
-    @patch('pubchempy.get_compounds', mock_get_compounds)
-    def test_water_2d(self):
+    def test_water_2d(self, monkeypatch):
+        monkeypatch.setattr(pubchempy, 'get_compounds', mock_get_compounds)
         water_geometry = geometry_from_pubchem('water', structure='2d')
-        self.water_natoms = len(water_geometry)
+        water_natoms_actual = len(water_geometry)
 
         water_natoms = 3
-        self.assertEqual(water_natoms, self.water_natoms)
+        assert water_natoms == water_natoms_actual
 
-        self.oxygen_z_1 = water_geometry[0][1][2]
-        self.oxygen_z_2 = water_geometry[1][1][2]
+        oxygen_z_1 = water_geometry[0][1][2]
+        oxygen_z_2 = water_geometry[1][1][2]
         z = 0
-        self.assertEqual(z, self.oxygen_z_1)
-        self.assertEqual(z, self.oxygen_z_2)
+        assert z == oxygen_z_1
+        assert z == oxygen_z_2
 
         with pytest.raises(ValueError, match='Incorrect value for the argument structure'):
             _ = geometry_from_pubchem('water', structure='foo')
 
     @pytest.mark.flaky(retries=3, delay=2, only_on=[pubchempy.ServerBusyError])
     def test_geometry_from_pubchem_live_api(self):
         water_geometry = geometry_from_pubchem('water')
-        self.assertEqual(len(water_geometry), 3)
+        assert len(water_geometry) == 3