def test_biased_checkerboard(self):
"""
Test that biased checkerboard (at one qubit) returns only one solution.
"""
sampler = GibbsSampler()
biased_checkerboard = IsingModel(J={(0, 1): 1, (1, 2): 1, (2, 3): 1, (3, 0): 1}, h={0: 2})
result = sampler.sample(biased_checkerboard, 10000)
solutions = [s.as_tuple for s in result]
assert (-1, 1, -1, 1) in solutions
assert len(solutions) == 1
# Enforce the opposite checkerboard
biased_checkerboard = IsingModel(J={(0, 1): 1, (1, 2): 1, (2, 3): 1, (3, 0): 1}, h={0: -2})
result = sampler.sample(biased_checkerboard, 10000)
solutions = [s.as_tuple for s in result]
assert (1, -1, 1, -1) in solutions
assert len(solutions) == 1
def test_unbiased_checkerboard(self):
"""
Test that checkerboard problem returns both valid solutions.
"""
sampler = GibbsSampler()
checkerboard = IsingModel(J={(0, 1): 1, (1, 2): 1, (2, 3): 1, (3, 0): 1}, h={})
result = sampler.sample(checkerboard, 10000)
solutions = [s.as_tuple for s in result]
assert (-1, 1, -1, 1) in solutions
assert (1, -1, 1, -1) in solutions
