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Add tests for quantities.constants #280

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77 changes: 76 additions & 1 deletion quantities/tests/test_constants.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,79 @@
from .. import units as pq
import numpy as np

from .. import constants as pc
from .. import units as pq
from .common import TestCase


class TestConstants(TestCase):

def assertRelativelyClose(self, q1, q2, rtol=1e-6):
# CODATA values are rounded, so relations between them hold only
# approximately
ratio = (q1 / q2).simplified
self.assertEqual(ratio.dimensionality, pq.dimensionless.dimensionality)
self.assertLess(abs(ratio.magnitude - 1), rtol)

def test_all_constants_simplify(self):
names = [
name for name in dir(pc)
if isinstance(getattr(pc, name), pc.UnitConstant)
]
self.assertGreater(len(names), 300)
for name in names:
with self.subTest(name=name):
magnitude = getattr(pc, name).simplified.magnitude
self.assertTrue(np.isfinite(magnitude))
self.assertNotEqual(magnitude, 0)

def test_units(self):
expected = {
'h': pq.J * pq.s,
'hbar': pq.J * pq.s,
'e': pq.C,
'k': pq.J / pq.K,
'N_A': 1 / pq.mol,
'R': pq.J / (pq.mol * pq.K),
'm_e': pq.kg,
'm_p': pq.kg,
'epsilon_0': pq.F / pq.m,
'mu_0': pq.N / pq.A**2,
'G': pq.m**3 / (pq.kg * pq.s**2),
'alpha': pq.dimensionless,
}
for name, units in expected.items():
with self.subTest(name=name):
self.assertEqual(
getattr(pc, name).simplified.dimensionality,
(1 * units).simplified.dimensionality,
)

def test_relations(self):
# reduced Planck constant: ħ = h/2π
self.assertRelativelyClose(pc.hbar, pc.h / (2 * np.pi))
# molar gas constant: R = N_A k
self.assertRelativelyClose(pc.R, pc.N_A * pc.k)
# Faraday constant: F = N_A e
self.assertRelativelyClose(pc.Faraday_constant, pc.N_A * pc.e)
# speed of light: ε₀μ₀c² = 1
self.assertRelativelyClose(pc.epsilon_0 * pc.mu_0 * pq.c**2, pq.dimensionless)
# impedance of vacuum: Z₀ = μ₀c
self.assertRelativelyClose(pc.Z_0, pc.mu_0 * pq.c)
# fine-structure constant: α = e²/4πε₀ħc
self.assertRelativelyClose(
pc.alpha, pc.e**2 / (4 * np.pi * pc.epsilon_0 * pc.hbar * pq.c)
)
# Bohr radius: a₀ = ħ/mₑcα
self.assertRelativelyClose(pc.a_0, pc.hbar / (pc.m_e * pq.c * pc.alpha))
# Bohr magneton: μ_B = eħ/2mₑ
self.assertRelativelyClose(pc.mu_B, pc.e * pc.hbar / (2 * pc.m_e))
# Rydberg constant: R∞ = α²mₑc/2h
self.assertRelativelyClose(
pc.R_infinity, pc.alpha**2 * pc.m_e * pq.c / (2 * pc.h)
)
# Stefan–Boltzmann constant: σ = 2π⁵k⁴/15h³c²
self.assertRelativelyClose(
pc.sigma, 2 * np.pi**5 * pc.k**4 / (15 * pc.h**3 * pq.c**2)
)
# electron volt: 1 eV = e × 1 V
self.assertRelativelyClose(pc.eV, pc.e * pq.V)
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