How to use the catalogue._get function in catalogue

def test_get_set():
    catalogue._set(("a", "b", "c"), "test")
    assert len(catalogue.REGISTRY) == 1
    assert ("a", "b", "c") in catalogue.REGISTRY
    assert catalogue.check_exists("a", "b", "c")
    assert catalogue.REGISTRY[("a", "b", "c")] == "test"
    assert catalogue._get(("a", "b", "c")) == "test"
    with pytest.raises(catalogue.RegistryError):
        catalogue._get(("a", "b", "d"))
    with pytest.raises(catalogue.RegistryError):
        catalogue._get(("a", "b", "c", "d"))
    catalogue._set(("x", "y", "z1"), "test1")
    catalogue._set(("x", "y", "z2"), "test2")
    assert catalogue._remove(("a", "b", "c")) == "test"
    catalogue._set(("x", "y2"), "test3")
    with pytest.raises(catalogue.RegistryError):
        catalogue._remove(("x", "y"))
    assert catalogue._remove(("x", "y", "z2")) == "test2"

def test_create_multi_namespace():
    test_registry = catalogue.create("x", "y")

    @test_registry.register("z")
    def z():
        pass

    items = test_registry.get_all()
    assert len(items) == 1
    assert items["z"] == z
    assert catalogue.check_exists("x", "y", "z")
    assert catalogue._get(("x", "y", "z")) == z

    @test_registry.register("a")
    def a():
        pass

    def b():
        pass

    test_registry.register("b", func=b)
    items = test_registry.get_all()
    assert len(items) == 2
    assert items["a"] == a
    assert items["b"] == b
    assert catalogue.check_exists("test", "a")
    assert catalogue.check_exists("test", "b")
    assert catalogue._get(("test", "a")) == a
    assert catalogue._get(("test", "b")) == b

    with pytest.raises(TypeError):
        # The decorator only accepts one argument
        @test_registry.register("x", "y")
        def x():
            pass