Add / update tests for predicates in stabiliser sim

Added a new unit test that checks we include the CliffordCircuitPredicate
only when we're running with a stabilizer simulator type (and not
when we have a statevector simulator).

Also update test_simulator to expect to fail on the predicate check in
process_circuit(), rather than breaking on get_result().

Author: isobelhooper

tests/integration/backend_test.py

@@ -56,7 +56,7 @@
     QuantinuumAPI,
     QuantinuumAPIError,
 )
-from pytket.extensions.quantinuum.backends.quantinuum import _ALL_GATES, GetResultFailed
+from pytket.extensions.quantinuum.backends.quantinuum import _ALL_GATES
 from pytket.predicates import CompilationUnit
 from pytket.wasm import WasmFileHandler
 
@@ -597,19 +597,17 @@ def test_simulator(
     assert sum(stab_counts.values()) == n_shots
     assert len(stab_counts) == 2
 
-    # test non-clifford circuit fails on stabilizer backend
-    # unfortunately the job is accepted, then fails, so have to check get_result
+    # test non-clifford circuit fails predicate check
+    # when run on stabilizer backend
     non_stab_circ = (
         Circuit(2, name="non_stab_circ").H(0).Rx(0.1, 0).CX(0, 1).measure_all()
     )
     non_stab_circ = stabilizer_backend.get_compiled_circuit(non_stab_circ)
-    broken_handle = stabilizer_backend.process_circuit(
-        non_stab_circ, n_shots, language=language
-    )
-
-    with pytest.raises(GetResultFailed) as _:
-        _ = stabilizer_backend.get_result(broken_handle)
 
+    with pytest.raises(CircuitNotValidError):
+        _ = stabilizer_backend.process_circuit(
+            non_stab_circ, n_shots, noisy_simulation=False, language=language
+        )
 
 @pytest.mark.skipif(skip_remote_tests, reason=REASON)
 @pytest.mark.timeout(120)

tests/unit/backend.py

@@ -0,0 +1,29 @@
+import pytest
+
+from pytket.extensions.quantinuum import QuantinuumAPIOffline, QuantinuumBackend
+from pytket.predicates import CliffordCircuitPredicate
+
+
+@pytest.mark.parametrize(
+    "simulator_type,should_have_clifford_predicate",
+    [
+        ("state-vector", False),
+        ("stabilizer", True),
+    ],
+)
+def test_clifford_circuits_for_stabilizer(
+    simulator_type: str,
+    should_have_clifford_predicate: bool,
+) -> None:
+    """Check that the stabilizer simulator restricts circuits to be Clifford circuits,
+    and the statevector simulator does not."""
+    qapi_offline = QuantinuumAPIOffline()
+    backend = QuantinuumBackend(
+        "H1-1E",
+        api_handler=qapi_offline,  # type: ignore
+        simulator=simulator_type,
+    )
+    required_predicates = backend.required_predicates
+    assert should_have_clifford_predicate == any(
+        isinstance(pred, CliffordCircuitPredicate) for pred in required_predicates
+    )