'``GetPackageVersion.run`` raises an exception if the supplied
``package_name`` is not installed in the supplied ``virtual_env``.'

def test_version_not_found(self):

    test_env = FilePath(self.mktemp())
    virtualenv = VirtualEnv(root=test_env)
    InstallVirtualEnv(virtualenv=virtualenv).run()
    step = GetPackageVersion(virtualenv=virtualenv, package_name='PackageWhichIsNotInstalled')
    self.assertRaises(Exception, step.run)
