@Override
    public Optional<FunctionDefinition> getFunctionDefinition(String name) {
        final String normalizedName = name.toUpperCase(Locale.ROOT);
        return Optional.ofNullable(normalizedFunctions.get(normalizedName));
    }
@Test
    void testGetInternalFunction() {
        assertThat(CoreModule.INSTANCE.getFunctionDefinition("$REPLICATE_ROWS$1"))
                .hasValueSatisfying(
                        def ->
                                assertThat(def)
                                        .asInstanceOf(type(BuiltInFunctionDefinition.class))
                                        .satisfies(
                                                builtInDef ->
                                                        assertThat(builtInDef.isInternal())
                                                                .isTrue())
                                        .satisfies(
                                                builtInDef ->
                                                        assertThat(builtInDef.getQualifiedName())
                                                                .isEqualTo("$REPLICATE_ROWS$1")));
    }