How to use the pint.context.Context function in Pint

def add_arg_ctxs(ureg):
    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[time]': -1})
    d = Context('lc')
    d.add_transformation(a, b, lambda ureg, x, n: ureg.speed_of_light / x / n)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.speed_of_light / x / n)

    ureg.add_context(d)

    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[current]': -1})
    d = Context('ab')
    d.add_transformation(a, b, lambda ureg, x: 1 / x)
    d.add_transformation(b, a, lambda ureg, x: 1 / x)

    ureg.add_context(d)

def add_argdef_ctxs(ureg):
    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[time]': -1})
    d = Context('lc', defaults=dict(n=1))
    assert d.defaults == dict(n=1)

    d.add_transformation(a, b, lambda ureg, x, n: ureg.speed_of_light / x / n)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.speed_of_light / x / n)

    ureg.add_context(d)

    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[current]': -1})
    d = Context('ab')
    d.add_transformation(a, b, lambda ureg, x: 1 / x)
    d.add_transformation(b, a, lambda ureg, x: 1 / x)

    ureg.add_context(d)

def add_arg_ctxs(ureg):
    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[time]': -1})
    d = Context('lc')
    d.add_transformation(a, b, lambda ureg, x, n: ureg.speed_of_light / x / n)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.speed_of_light / x / n)

    ureg.add_context(d)

    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[current]': -1})
    d = Context('ab')
    d.add_transformation(a, b, lambda ureg, x: 1 / x)
    d.add_transformation(b, a, lambda ureg, x: 1 / x)

    ureg.add_context(d)

def test_warnings(self):

        ureg = UnitRegistry()

        th = TestHandler()
        logger.addHandler(th)

        add_ctxs(ureg)

        d = Context('ab')
        ureg.add_context(d)

        self.assertEqual(len(th.buffer), 1)
        self.assertIn("ab", str(th.buffer[-1]['message']))

        d = Context('ab1', aliases=('ab',))
        ureg.add_context(d)

        self.assertEqual(len(th.buffer), 2)
        self.assertIn("ab", str(th.buffer[-1]['message']))

def test_warnings(self):

        ureg = UnitRegistry()

        with self.capture_log() as buffer:
            add_ctxs(ureg)

            d = Context('ab')
            ureg.add_context(d)

            self.assertEqual(len(buffer), 1)
            self.assertIn("ab", str(buffer[-1]))

            d = Context('ab1', aliases=('ab',))
            ureg.add_context(d)

            self.assertEqual(len(buffer), 2)
            self.assertIn("ab", str(buffer[-1]))

def add_argdef_ctxs(ureg):
    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[time]': -1})
    d = Context('lc', defaults=dict(n=1))
    assert d.defaults == dict(n=1)

    d.add_transformation(a, b, lambda ureg, x, n: ureg.speed_of_light / x / n)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.speed_of_light / x / n)

    ureg.add_context(d)

    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[current]': 1})
    d = Context('ab')
    d.add_transformation(a, b, lambda ureg, x: ureg.ampere * ureg.meter / x)
    d.add_transformation(b, a, lambda ureg, x: ureg.ampere * ureg.meter / x)

    ureg.add_context(d)

def test_parse_parameterized(self):
        a = Context.__keytransform__(UnitsContainer({'[time]': -1.}), UnitsContainer({'[length]': 1.}))
        b = Context.__keytransform__(UnitsContainer({'[length]': 1.}), UnitsContainer({'[time]': -1.}))

        s = ['@context(n=1) longcontextname',
             '[length] <-> 1 / [time]: n * c / value']

        c = Context.from_lines(s)
        self.assertEqual(c.defaults, {'n': 1})
        self.assertEqual(set(c.funcs.keys()), set((a, b)))
        self._test_ctx(c)

        # If the variable is not present in the definition, then raise an error
        s = ['@context(n=1) longcontextname',
             '[length] <-> 1 / [time]: c / value']
        self.assertRaises(ValueError, Context.from_lines, s)

def add_sharedargdef_ctxs(ureg):
    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[time]': -1})
    d = Context('lc', defaults=dict(n=1))
    assert d.defaults == dict(n=1)

    d.add_transformation(a, b, lambda ureg, x, n: ureg.speed_of_light / x / n)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.speed_of_light / x / n)

    ureg.add_context(d)

    a, b = UnitsContainer({'[length]': 1}), UnitsContainer({'[current]': 1})
    d = Context('ab', defaults=dict(n=0))
    d.add_transformation(a, b, lambda ureg, x, n: ureg.ampere * ureg.meter * n / x)
    d.add_transformation(b, a, lambda ureg, x, n: ureg.ampere * ureg.meter * n / x)

    ureg.add_context(d)

def add_ctxs(ureg):
    a, b = UnitsContainer({"[length]": 1}), UnitsContainer({"[time]": -1})
    d = Context("lc")
    d.add_transformation(a, b, lambda ureg, x: ureg.speed_of_light / x)
    d.add_transformation(b, a, lambda ureg, x: ureg.speed_of_light / x)

    ureg.add_context(d)

    a, b = UnitsContainer({"[length]": 1}), UnitsContainer({"[current]": 1})
    d = Context("ab")
    d.add_transformation(a, b, lambda ureg, x: ureg.ampere * ureg.meter / x)
    d.add_transformation(b, a, lambda ureg, x: ureg.ampere * ureg.meter / x)

    ureg.add_context(d)