Spawn threads in tests

tests/noise_model_test.py

@@ -303,6 +303,8 @@ def test_to_dict(tmpdir_factory) -> None:
 @pytest.mark.high_compute
 def test_transpiler_backend() -> None:
 
+    mp.set_start_method("spawn", force=True)
+
     circuit = Circuit(3)
     for _ in range(32):
         circuit.ZZMax(0, 1).ZZMax(1, 2)

tests/zne_test.py

@@ -50,6 +50,7 @@
 from qermit.zero_noise_extrapolation.zne import gen_noise_scaled_mitex
 from qermit.noise_model import TranspilerBackend, PauliErrorTranspile
 from itertools import product
+import multiprocessing as mp
 
 n_qubits = 2
 
@@ -848,6 +849,8 @@ def test_end_to_end_noise_scaled_mitex():
 @pytest.mark.high_compute
 def test_end_to_end_noise_aware_zne_mitex_starting_from_ptm() -> None:
 
+    mp.set_start_method("spawn", force=True)
+
     # Here we are creating the PTM for a noise model acting
     # XI with rate 0.1
     ptm = np.diag([1, 1, 1, 1, 1, 1, 1, 1, 0.8, 0.8, 0.8, 0.8, 0.8, 0.8, 0.8, 0.8])
@@ -907,6 +910,8 @@ def test_end_to_end_noise_aware_zne_mitex_starting_from_ptm() -> None:
 @pytest.mark.high_compute
 def test_end_to_end_noise_aware_zne_mitex():
 
+    mp.set_start_method("spawn", force=True)
+
     error_rate = 0.1
     error_distribution = ErrorDistribution(
         distribution={(Pauli.X, Pauli.I): error_rate}