From 29ca5044e949f461266e4b9cfb2861cb6871591f Mon Sep 17 00:00:00 2001
From: MatteoRobbiati <robbiati.matteo@gmail.com>
Date: Thu, 30 Jan 2025 11:35:02 +0100
Subject: [PATCH] test: add conftest and first observable test

---
 tests/conftest.py         | 66 +++++++++++++++++++++++++++++++++++++++
 tests/test_observables.py | 47 ++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 tests/conftest.py
 create mode 100644 tests/test_observables.py

diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..0a18bfa
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,66 @@
+"""conftest.py.
+
+Pytest fixtures.
+"""
+
+import sys
+
+import pytest
+
+# backends to be tested
+# TODO: add cutensornet and quimb here as well
+BACKENDS = ["qmatchatea"]
+
+
+def get_backend(backend_name):
+
+    from qibotn.backends.qmatchatea import QMatchaTeaBackend
+
+    NAME2BACKEND = {
+        "qmatchatea": QMatchaTeaBackend,
+    }
+
+    return NAME2BACKEND[backend_name]()
+
+
+AVAILABLE_BACKENDS = []
+for backend_name in BACKENDS:
+    try:
+        _backend = get_backend(backend_name)
+        AVAILABLE_BACKENDS.append(backend_name)
+    except (ModuleNotFoundError, ImportError):
+        pass
+
+
+def pytest_runtest_setup(item):
+    ALL = {"darwin", "linux"}
+    supported_platforms = ALL.intersection(mark.name for mark in item.iter_markers())
+    plat = sys.platform
+    if supported_platforms and plat not in supported_platforms:  # pragma: no cover
+        # case not covered by workflows
+        pytest.skip(f"Cannot run test on platform {plat}.")
+
+
+@pytest.fixture
+def backend(backend_name):
+    yield get_backend(backend_name)
+
+
+def pytest_runtest_setup(item):
+    ALL = {"darwin", "linux"}
+    supported_platforms = ALL.intersection(mark.name for mark in item.iter_markers())
+    plat = sys.platform
+    if supported_platforms and plat not in supported_platforms:  # pragma: no cover
+        # case not covered by workflows
+        pytest.skip(f"Cannot run test on platform {plat}.")
+
+
+def pytest_configure(config):
+    config.addinivalue_line("markers", "linux: mark test to run only on linux")
+
+
+def pytest_generate_tests(metafunc):
+    module_name = metafunc.module.__name__
+
+    if "backend_name" in metafunc.fixturenames:
+        metafunc.parametrize("backend_name", AVAILABLE_BACKENDS)
diff --git a/tests/test_observables.py b/tests/test_observables.py
new file mode 100644
index 0000000..d89c6f9
--- /dev/null
+++ b/tests/test_observables.py
@@ -0,0 +1,47 @@
+import math
+import random
+
+import pytest
+from qibo import Circuit, construct_backend, gates, hamiltonians
+from qibo.symbols import X, Z
+
+
+def build_observable(nqubits):
+    """Helper function to construct a target observable."""
+    hamiltonian_form = 0
+    for i in range(nqubits):
+        hamiltonian_form += 0.5 * X(i % nqubits) * Z((i + 1) % nqubits)
+
+    hamiltonian = hamiltonians.SymbolicHamiltonian(form=hamiltonian_form)
+    return hamiltonian, hamiltonian_form
+
+
+def build_circuit(nqubits, nlayers, seed=42):
+    """Helper function to construct a layered quantum circuit."""
+    random.seed(seed)
+
+    circ = Circuit(nqubits)
+    for _ in range(nlayers):
+        for q in range(nqubits):
+            circ.add(gates.RY(q=q, theta=random.uniform(-math.pi, math.pi)))
+            circ.add(gates.RZ(q=q, theta=random.uniform(-math.pi, math.pi)))
+        [circ.add(gates.CNOT(q % nqubits, (q + 1) % nqubits) for q in range(nqubits))]
+    circ.add(gates.M(*range(nqubits)))
+    return circ
+
+
+@pytest.mark.parametrize("nqubits", [2, 5, 10])
+def test_observable_expval(backend, nqubits):
+    numpy_backend = construct_backend("numpy")
+    ham, ham_form = build_observable(nqubits)
+    circ = build_circuit(nqubits=nqubits, nlayers=1)
+
+    exact_expval = numpy_backend.calculate_expectation_state(
+        hamiltonian=ham,
+        state=circ().state(),
+        normalize=False,
+    )
+
+    tn_expval = backend.expectation(circuit=circ, observable=ham_form)
+
+    assert math.isclose(exact_expval, tn_expval, abs_tol=1e-7)