Tests for c++ objects against python implementations

tests/approvals/test_pauli_string.py

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+"""Test pauli c++ objects against python implementations."""
+
+import itertools as it
+
+import numpy as np
+import pytest
+
+import fast_pauli._fast_pauli as fp
+import fast_pauli.pypauli.operations as pp
+
+
+@pytest.fixture
+def sample_strings() -> list[str]:
+    """Provide sample strings for testing."""
+    strings = it.chain(
+        ["I", "X", "Y", "Z"],
+        it.permutations("IXYZ", 2),
+        it.permutations("IXYZ", 3),
+        ["ZIZI", "YZYZ", "XYZXYZ", "ZZZIII", "XYIZXYZ", "XXIYYIZZ", "ZIXIZYXX"],
+    )
+    return list(map("".join, strings))
+
+
+def test_pauli_object(paulis: dict) -> None:
+    """Test that C++ Pauli object is numerically equivalent to Python Pauli object."""
+    # ideally, here we want to test against corresponding Pauli struct
+    # from python land, but currently we don't have one
+    for c in ["I", "X", "Y", "Z"]:
+        p = fp.Pauli(c)
+        np.testing.assert_array_equal(
+            np.array(p.to_tensor()),
+            paulis[c],
+        )
+        np.testing.assert_string_equal(str(p), c)
+
+
+def test_pauli_string_representations(sample_strings: list[str]) -> None:
+    """Test that C++ PauliString is numerically equivalent to Python PauliString."""
+    for s in sample_strings:
+        pcpp = fp.PauliString(s)
+        ppy = pp.PauliString(s)
+
+        np.testing.assert_allclose(
+            pcpp.to_tensor(),
+            ppy.dense(),
+            atol=1e-15,
+        )
+        np.testing.assert_string_equal(str(pcpp), str(ppy))
+        assert pcpp.dims == ppy.dim
+        assert pcpp.weight == ppy.weight
+
+
+def test_pauli_string_apply_batch(sample_strings: list[str]) -> None:
+    """Test that C++ PauliString is numerically equivalent to Python PauliString."""
+    rng = np.random.default_rng(321)
+
+    for s in sample_strings:
+        n = 2 ** len(s)
+        psis = rng.random((n, 42))
+
+        np.testing.assert_allclose(
+            np.array(fp.PauliString(s).apply_batch(psis.tolist())),
+            pp.PauliString(s).multiply(psis),
+            atol=1e-15,
+        )
+
+
+if __name__ == "__main__":
+    pytest.main([__file__])