@Test
	public void testInitWithFallbackMsgResponse() {
		FallbackProperties fallbackProperties = mock(FallbackProperties.class);
		when(gatewayProperties.getFallback()).thenReturn(fallbackProperties);
		when(fallbackProperties.getMode()).thenReturn(ConfigConstants.FALLBACK_MSG_RESPONSE);
		when(fallbackProperties.getResponseStatus()).thenReturn(200);
		when(fallbackProperties.getContentType()).thenReturn(MediaType.APPLICATION_JSON.toString());
		when(fallbackProperties.getResponseBody()).thenReturn("test");
		config.init();
		Mono<ServerResponse> responseMono = GatewayCallbackManager.getBlockHandler()
				.handleRequest(mock(ServerWebExchange.class), null);
		Assert.assertEquals(200, Objects.requireNonNull(responseMono.block()).statusCode().value());
	}
Tests the initialization method when the fallback mode is set to return a custom response message.
Verifies that the response status, content type, and body match the expected values.
spring-cloud-alibaba-starters/spring-cloud-alibaba-sentinel-gateway/src/test/java/com/alibaba/cloud/sentinel/gateway/scg/SentinelSCGAutoConfigurationTest.java