add testfile for lowlevel QNN

tests/qnn/lowlevel_qnn/test_lowlevel_qnn.py

@@ -0,0 +1,65 @@
+import pytest
+import numpy as np
+
+
+from squlearn import Executor
+from squlearn.encoding_circuit import ChebyshevPQC
+from squlearn.observables import SummedPaulis
+from squlearn.qnn.lowlevel_qnn import LowLevelQNN
+
+
+def get_values(framework):
+    executor = Executor(framework)
+    pqc = ChebyshevPQC(4, 2)
+    obs1 = SummedPaulis(4)
+    obs2 = SummedPaulis(4)
+
+    llqnn = LowLevelQNN(pqc, [obs1, obs2], executor=executor, num_features=2)
+
+    np.random.seed(42)
+    param = np.random.rand(2, llqnn.num_parameters)
+    param_pbs = np.random.rand(2, llqnn.num_parameters_observable)
+
+    return llqnn.evaluate(
+        [[0.1, 0.2], [0.3, 0.4]],
+        param,
+        param_pbs,
+        "f",
+        "dfdp",
+        "dfdx",
+        "var",
+        (llqnn.parameters[0],),
+        (llqnn.parameters_operator[0],),
+    )
+
+
+def test_backends_consistency():
+    """Tests that different derivatives computed with different frameworks are consistent."""
+
+    values_qiskit = get_values("qiskit")
+    values_pennylane = get_values("pennylane")
+    values_qulacs = get_values("qulacs")
+
+    for k in ["f", "dfdp", "dfdx", "var"]:
+        assert np.allclose(values_qiskit[k], values_pennylane[k])
+        assert np.allclose(values_qiskit[k], values_qulacs[k])
+
+    qiskit_keys = sorted(list(values_qiskit.keys()), key=str)
+    pennylane_keys = sorted(list(values_pennylane.keys()), key=str)
+    qulacs_keys = sorted(list(values_qulacs.keys()), key=str)
+
+    qiskit_param_key = qiskit_keys[0]
+    pennylane_param_key = pennylane_keys[2]
+    qulacs_param_key = qulacs_keys[2]
+
+    qiskit_param_op_key = qiskit_keys[1]
+    pennylane_param_op_key = pennylane_keys[3]
+    qulacs_param_op_key = qulacs_keys[3]
+
+    assert np.allclose(values_qiskit[qiskit_param_key], values_pennylane[pennylane_param_key])
+    assert np.allclose(values_qiskit[qiskit_param_key], values_qulacs[qulacs_param_key])
+
+    assert np.allclose(
+        values_qiskit[qiskit_param_op_key], values_pennylane[pennylane_param_op_key]
+    )
+    assert np.allclose(values_qiskit[qiskit_param_op_key], values_qulacs[qulacs_param_op_key])