Add test.

recirq/qcqmc/bitstrings_test.py

@@ -0,0 +1,20 @@
+import numpy as np
+import pytest
+import scipy
+
+from recirq.qcqmc.bitstrings import get_bitstrings_a_b
+
+
+def test_get_bitstrings_a_b():
+    with pytest.raises(NotImplementedError):
+        list(get_bitstrings_a_b(n_orb=4, n_elec=3))
+
+    bitstrings = np.array(list(get_bitstrings_a_b(n_orb=4, n_elec=4)))
+
+    assert bitstrings.shape[0] == scipy.special.binom(4, 2) ** 2
+    assert bitstrings.shape[1] == 2 * 4  # n_qubits columns = 2 * n_orb.
+    hamming_weight_left = np.sum(bitstrings[:, 0:4], axis=1)
+    hamming_weight_right = np.sum(bitstrings[:, 4:8], axis=1)
+
+    assert np.all(hamming_weight_left == 2)
+    assert np.all(hamming_weight_right == 2)