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+from functools import reduce

+

+from hypothesis import given

+import hypothesis.strategies as st

+import numpy as np

+import pytest

+

+import qsim.gate

+import qsim.state

+from qsim.measurement import measure

+

+from .common import (

+    classical_bitstrings,

+    n_qubits,

+    rng,

+    valid_states,

+)

+

+classical_states = classical_bitstrings.map(qsim.state.from_classical)

+arbitrary_qubit = n_qubits.flatmap(lambda n: st.integers(0, n - 1))

+

+

+@given(rng, arbitrary_qubit, classical_bitstrings)

+def test_classical_measurement(rng, qubit, bitstring):

+    """Test measurements on "classical" states.

+

+    The outcome of a measurement on qubit 'n' of a classical state (i.e. a state

+    constructed from a classical bitstring) is the value of the n-th bit of

+    the bitstring.

+    """

+    classical_state = qsim.state.from_classical(bitstring)

+    # [::-1] because qubits are indexed from the least-significant,

+    # but bitstring are written most-significant bit first.

+    expected_outcome = bool(int(bitstring[::-1][qubit]))

+    outcome, _ = measure(rng, qubit, classical_state)

+    assert outcome == expected_outcome

+

+

+@given(rng, arbitrary_qubit, valid_states)

+def test_subsequent_measurement(rng, qubit, ket):

+    """Test that subsequent measurements of the same qubit yield the same outcome."""

+    outcome, measured_ket = measure(rng, qubit, ket)

+    outcome2, measured_ket2 = measure(rng, qubit, measured_ket)

+    assert np.allclose(measured_ket, measured_ket2)

+    assert outcome == outcome2