Some miscellaneous fixes

Related to https://build.spring.io/browse/INT-MASTERSPRING40-JOB1-1271

* Fix race condition with subscription in the `FluxMessageChannel`:
rely on the `doOnRequest()` to start producing from upstream publishers
* Remove `SourcePollingChannelAdapterTests` since
`Class.getDeclaredConstructor().newInstance()` doesn't rethrow an exception as is
but wrap it into the `InvocationTargetException`.
This is probably the main reason to deprecate a regular `Class.newInstance()`
* Use `LettuceConnectionFactory.setEagerInitialization(true)` in the `RedisAvailableRule`
to avoid possible dead lock with lazy init
* Adjust Redis tests for new `RedisAvailableRule` behavior

spring-integration-core/src/test/java/org/springframework/integration/endpoint/SourcePollingChannelAdapterTests.java

@@ -1,116 +0,0 @@
-/*
- * Copyright 2020 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.integration.endpoint;
-
-import static org.assertj.core.api.Assertions.assertThat;
-
-import java.io.IOException;
-import java.lang.reflect.UndeclaredThrowableException;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.TimeUnit;
-
-import org.aopalliance.intercept.MethodInterceptor;
-import org.junit.jupiter.api.Test;
-
-import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.context.annotation.Bean;
-import org.springframework.context.annotation.Configuration;
-import org.springframework.integration.config.EnableIntegration;
-import org.springframework.integration.core.MessageSource;
-import org.springframework.integration.dsl.IntegrationFlow;
-import org.springframework.integration.dsl.IntegrationFlows;
-import org.springframework.integration.dsl.Pollers;
-import org.springframework.lang.Nullable;
-import org.springframework.messaging.Message;
-import org.springframework.test.annotation.DirtiesContext;
-import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
-
-/**
- * @author Gary Russell
- * @since 4.3.23
- *
- */
-@SpringJUnitConfig
-@DirtiesContext
-public class SourcePollingChannelAdapterTests {
-
-	@Autowired
-	Config config;
-
-	@Test
-	void undeclaredCheckedException() throws InterruptedException {
-		assertThat(this.config.latchl.await(10, TimeUnit.SECONDS)).isTrue();
-		assertThat(this.config.caught).isInstanceOf(UndeclaredThrowableException.class);
-	}
-
-	@Configuration
-	@EnableIntegration
-	public static class Config {
-
-		volatile Exception caught;
-
-		volatile CountDownLatch latchl = new CountDownLatch(1);
-
-		@Bean
-		public IntegrationFlow flow() {
-			return IntegrationFlows.from(new BadMessageSource(), e -> e.poller(Pollers.fixedDelay(500)
-					.advice(exceptionCaptor())))
-					.nullChannel();
-		}
-
-		private MethodInterceptor exceptionCaptor() {
-			return invocation -> {
-				try {
-					return invocation.proceed();
-				}
-				catch (Exception e) {
-					Config.this.caught = e;
-					throw e;
-				}
-				finally {
-					Config.this.latchl.countDown();
-				}
-			};
-		}
-
-	}
-
-	public static class BadMessageSource implements MessageSource<String> {
-
-		@Override
-		@Nullable
-		public Message<String> receive() {
-			try {
-				Foo.class.newInstance();
-			}
-			catch (InstantiationException | IllegalAccessException e) {
-			}
-			return null;
-		}
-
-	}
-
-	public static class Foo {
-
-		public Foo() throws IOException {
-			throw new IOException();
-		}
-
-	}
-
-}
-