How to use the rospkg.os_detect.OsDetect function in rospkg

def test_InstallerContext_ctor():
    from rosdep2.installers import InstallerContext
    from rospkg.os_detect import OsDetect

    context = InstallerContext()
    assert context.get_os_detect() is not None
    assert isinstance(context.get_os_detect(), OsDetect)

    detect = OsDetect()
    context = InstallerContext(detect)
    assert context.get_os_detect() == detect
    assert len(context.get_installer_keys()) == 0
    assert len(context.get_os_keys()) == 0

    context.verbose = True
    assert context.get_os_detect() == detect
    assert len(context.get_installer_keys()) == 0
    assert len(context.get_os_keys()) == 0

def test_Fedora_variable_lookup_key():
    from rosdep2 import InstallerContext
    from rosdep2.platforms import pip, redhat, source
    from rosdep2.platforms.redhat import DNF_INSTALLER, YUM_INSTALLER

    from rospkg.os_detect import OsDetect, OS_FEDORA
    os_detect_mock = Mock(spec=OsDetect)
    os_detect_mock.get_name.return_value = 'fedora'
    os_detect_mock.get_codename.return_value = 'heisenbug'
    os_detect_mock.get_version.return_value = '20'

    # create our test fixture.  use most of the default toolchain, but
    # replace the apt installer with one that we can have more fun
    # with.  we will do all tests with ubuntu lucid keys -- other
    # tests should cover different resolution cases.
    context = InstallerContext(os_detect_mock)
    pip.register_installers(context)
    redhat.register_installers(context)
    source.register_installers(context)
    redhat.register_platforms(context)

    assert ('fedora', 'heisenbug') == context.get_os_name_and_version()

def test_InstallerContext_installers():
    from rosdep2.installers import InstallerContext, Installer
    from rospkg.os_detect import OsDetect
    detect = OsDetect()
    context = InstallerContext(detect)
    context.verbose = True

    key = 'fake-apt'
    try:
        installer = context.get_installer(key)
        assert False, 'should have raised: %s' % (installer)
    except KeyError:
        pass

    class Foo:
        pass

    class FakeInstaller(Installer):
        pass

def test_InstallerContext_os_installers():
    from rosdep2.installers import InstallerContext, Installer
    from rospkg.os_detect import OsDetect
    detect = OsDetect()
    context = InstallerContext(detect)
    context.verbose = True

    os_key = 'ubuntu'
    try:
        context.get_os_installer_keys(os_key)
        assert False, 'should have raised'
    except KeyError:
        pass
    try:
        context.get_default_os_installer_key(os_key)
        assert False, 'should have raised'
    except KeyError:
        pass
    try:
        context.add_os_installer_key(os_key, 'fake-key')