def install_pip(self, package, save=True, save_dev=False):
        """Installs a pip package.

        :param save: if `True`, pins the package to the Hydrogen requirements
            YAML file.
        :param save_dev: if `True`, pins the package as a development
            dependency to the Hydrogen requirements YAML file.
        :param return: a **single** :class:`Requirement` object, representing
            the installed version of the given package.
        """
        requirement = Requirement.coerce(package)
        click.echo("pip install " + requirement.package)
        cmd = envoy.run("pip install {}".format(str(requirement)))
        if cmd.status_code == 0:
            installed_packages = get_installed_pypackages()
            package = installed_packages[requirement.package]
            requirement.version = "=={}".format(package.version)
            if save:
                self.requirements["all"].add(requirement)
            if save_dev:
                self.requirements["dev"].add(requirement)
            if save or save_dev:
                self.requirements.save()
            return requirement
        else:
            fatal(cmd.std_err)
def test_deviation():
    n1, n2 = symbols('n1, n2')
    r1 = Ray3D(Point3D(-1, -1, 1), Point3D(0, 0, 0))
    n = Matrix([0, 0, 1])
    i = Matrix([-1, -1, -1])
    normal_ray = Ray3D(Point3D(0, 0, 0), Point3D(0, 0, 1))
    P = Plane(Point3D(0, 0, 0), normal_vector=[0, 0, 1])
    assert deviation(r1, 1, 1, normal=n) == 0
    assert deviation(r1, 1, 1, plane=P) == 0
    assert deviation(r1, 1, 1.1, plane=P).evalf(3) + 0.119 < 1e-3
    assert deviation(i, 1, 1.1, normal=normal_ray).evalf(3) + 0.119 < 1e-3
    assert deviation(r1, 1.33, 1, plane=P) is None  # TIR
    assert deviation(r1, 1, 1, normal=[0, 0, 1]) == 0
    assert deviation([-1, -1, -1], 1, 1, normal=[0, 0, 1]) == 0
    assert ae(deviation(0.5, 1, 2), -0.25793, 5)
    assert ae(deviation(0.5, 2, 1), 0.78293, 5)