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"""Test constraint solver."""
from gaphas.constraint import EqualsConstraint, LessThanConstraint
from gaphas.solver import REQUIRED, MultiConstraint, Solver, Variable
from gaphas.solver.constraint import Constraint, ContainsConstraints
def test_solver_implements_constraint_protocol():
solver = Solver()
assert isinstance(solver, Constraint)
assert isinstance(solver, ContainsConstraints)
def test_weakest_list_order():
solver = Solver()
a = Variable(1, 30)
b = Variable(2, 10)
c_eq = EqualsConstraint(a, b)
solver.add_constraint(c_eq)
a.value = 4
b.value = 5
assert c_eq.weakest() == b
a.value = 6
assert c_eq.weakest() == b
b.value = 6
assert c_eq.weakest() == a
def test_minimal_size_constraint():
solver = Solver()
v1 = Variable(0)
v2 = Variable(10)
v3 = Variable(10)
c1 = EqualsConstraint(a=v2, b=v3)
c2 = LessThanConstraint(smaller=v1, bigger=v3, delta=10)
solver.add_constraint(c1)
solver.add_constraint(c2)
# Check everything is ok on start
solver.solve()
assert 0 == v1
assert 10 == v2
assert 10 == v3
# Change v1 to 2, after solve it should be 0 again due to LT constraint
v1.value = 2
solver.solve()
assert 0 == v1
assert 10 == v2
assert 10 == v3
# Change v3 to 20, after solve v2 will follow thanks to EQ constraint
v3.value = 20
solver.solve()
assert 0 == v1
assert 20 == v2
assert 20 == v3
# Change v3 to 0, after solve it should be 10 due to LT.delta = 10, v2
# should also be 10 due to EQ constraint
v3.value = 0
solver.solve()
assert 0 == v1
assert 10 == v2
assert 10 == v3
def test_constraints_can_not_be_resolved():
solver = Solver()
a = Variable()
b = Variable()
c = Variable(40, strength=REQUIRED)
d = Variable(30, strength=REQUIRED)
solver.add_constraint(EqualsConstraint(a, b))
solver.add_constraint(EqualsConstraint(a, c))
solver.add_constraint(EqualsConstraint(b, d))
solver.solve()
assert a.value == 40.0
assert b.value == 30.0
def test_notify_for_nested_constraint():
events = []
solver = Solver()
a = Variable()
b = Variable()
nested = EqualsConstraint(a, b)
multi = MultiConstraint(nested)
solver.add_constraint(multi)
solver.solve()
def handler(constraint):
events.append(constraint)
solver.add_handler(handler)
a.value = 10
solver.solve()
assert multi in events
assert nested not in events
def test_notify_for_double_nested_constraint():
events = []
solver = Solver()
a = Variable()
b = Variable()
nested = EqualsConstraint(a, b)
multi = MultiConstraint(nested)
outer = MultiConstraint(multi)
solver.add_constraint(outer)
solver.solve()
def handler(constraint):
events.append(constraint)
solver.add_handler(handler)
a.value = 10
solver.solve()
assert outer in events
def test_needs_solving():
solver = Solver()
a = Variable()
b = Variable()
eq = EqualsConstraint(a, b)
solver.add_constraint(eq)
assert solver.needs_solving
solver.solve()
assert not solver.needs_solving
a.value = 3
assert solver.needs_solving
solver.solve()
assert not solver.needs_solving
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