Add unit tests for Multitensor dual basis arg

Author: mhucka

src/openfermion/contrib/representability/_multitensor_test.py

@@ -94,6 +94,33 @@ def test_add_dualelement():
     mt.add_dual_elements(dbe)
     assert len(mt.dual_basis) == 1
 
+    dbe2 = DualBasisElement()
+    dbe2.add_element('b', (0, 1, 2), 5)
+    mt.add_dual_elements(dbe2)
+    assert len(mt.dual_basis) == 2
+
+    A, bias, scalar = mt.synthesize_dual_basis()
+    assert A.shape[0] == 2
+    # Verify that the elements are correctly added as DualBasisElements
+    # and not as their internal tuples (which would cause synthesis to fail).
+    assert isinstance(mt.dual_basis[0], DualBasisElement)
+    assert isinstance(mt.dual_basis[1], DualBasisElement)
+
+
+def test_multitensor_init_isolation():
+    # Test that different MultiTensor instances don't share the same dual_basis.
+    a = np.random.random((2, 2))
+    at = Tensor(tensor=a, name='a')
+    mt1 = MultiTensor([at])
+    mt2 = MultiTensor([at])
+
+    dbe = DualBasisElement()
+    dbe.add_element('a', (0, 0), 1.0)
+    mt1.add_dual_elements(dbe)
+
+    assert len(mt1.dual_basis) == 1
+    assert len(mt2.dual_basis) == 0
+
 
 def test_synthesis_element():
     a = np.random.random((5, 5))