Conditioned DMRG unittests (oimeitei#44)

* Added unittest for BE-DMRG (Insensitive to imports)

* Remove redundant imports.

---------

Co-authored-by: Shaun Weatherly <shaunrw@telemachus.mit.edu>

tests/dmrg_molBE_test.py

@@ -0,0 +1,52 @@
+"""
+This script tests the QuEmb to block2 interface for performing ground state BE-DMRG. 
+Author(s): Shaun Weatherly
+"""
+
+import os
+import unittest
+import tempfile
+from pyscf import gto, scf
+from molbe import fragpart, BE
+
+class TestBE_DMRG(unittest.TestCase):
+    try:
+        from pyscf import dmrgscf
+    except ImportError:
+        dmrgscf=None
+
+    @unittest.skipIf(dmrgscf is None, "Module `pyscf.dmrgscf` not imported correctly.")
+    def test_h8_sto3g_pipek(self):
+        mol = gto.M()
+        mol.atom = [['H', (0.,0.,i*1.2)] for i in range(8)]
+        mol.basis = 'sto-3g'
+        mol.charge = 0
+        mol.spin = 0
+        mol.build()
+        self.molecular_DMRG_test(mol, 'be1', 100, 'H8 (BE1)', 'hchain_simple', -4.20236532)
+
+    def molecular_DMRG_test(self, mol, be_type, maxM, test_name, frag_type, target, delta = 1e-4):
+        with tempfile.TemporaryDirectory() as tmp:
+            mf = scf.RHF(mol); mf.kernel()
+            fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mol)
+            mybe = BE(mf, fobj, lo_method='pipek', pop_method='lowdin')
+            mybe.oneshot(solver='block2', 
+                        scratch_dir=str(tmp),
+                        maxM=int(maxM),
+                        maxIter=30,
+                        force_cleanup=True)
+            self.assertAlmostEqual(mybe.ebe_tot, target,
+                                msg = "BE Correlation Energy (Chem. Pot. Optimization) for " + test_name
+                                + " does not match the expected correlation energy!", delta = delta)
+            tmpfiles = []
+            for path, dir_n, file_n in os.walk(tmp, topdown=True):
+                for n in file_n:
+                    if n.startswith('F.') or n.startswith('FCIDUMP') or n.startswith('node'):
+                        tmpfiles.append(n)
+            try:
+                assert len(tmpfiles) == 0
+            except Exception as inst:
+                print(f"DMRG tempfiles not cleared correctly in {test_name}:\n", inst, tmpfiles)
+
+if __name__ == '__main__':
+    unittest.main()