def test_pstring_collection_str():
x = PauliString(spec="X")
iz = PauliString(spec="IZ")
pcol = PauliStringCollection(x, iz)
assert str(pcol) == "X(0) + Z(1)"
xz = PauliString(spec="XZ", coeff=-2.4)
pcol.add(xz)
assert str(pcol) == "X(0) + Z(1) + (-2.4+0j)*X(0)*Z(1)"
def test_pstring_collection_add():
pcol = PauliStringCollection()
a = PauliString(spec="ZZ")
assert pcol.can_add(a)
pcol.add(a)
assert pcol.elements == [a]
b = PauliString(spec="ZIXZ")
assert pcol.can_add(b)
pcol.add(b)
assert pcol.elements == [a, b]
assert pcol.can_add(a)
pcol.add(a)
assert pcol.elements == [a, a, b]
c = PauliString(spec="YY")
assert not pcol.can_add(c)
with pytest.raises(ValueError, match="Cannot add PauliString"):
pcol.add(c)