Disable ReactorResourceFactory use of global resources in tests

Add `ContextCustomizerFactory` to automatically disable the use of
`ReactorResourceFactory` global resources in tests.

Fixes gh-38199

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactor/netty/DisableReactorResourceFactoryGlobalResourcesContextCustomizerFactoryTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2012-2024 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.boot.test.web.reactor.netty;
+
+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.http.client.ReactorResourceFactory;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DisableReactorResourceFactoryGlobalResourcesContextCustomizerFactory}.
+ *
+ * @author Phillip Webb
+ */
+@SpringJUnitConfig
+class DisableReactorResourceFactoryGlobalResourcesContextCustomizerFactoryTests {
+
+	@Autowired
+	private ReactorResourceFactory reactorResourceFactory;
+
+	@Test
+	void disablesUseGlobalResources() {
+		assertThat(this.reactorResourceFactory.isUseGlobalResources()).isFalse();
+	}
+
+	@Configuration
+	static class Config {
+
+		@Bean
+		ReactorResourceFactory reactorResourceFactory() {
+			return new ReactorResourceFactory();
+		}
+
+	}
+
+}