diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/AbstractMockServerSpec.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/AbstractMockServerSpec.java
index 4725dd06a6..eda1688651 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/AbstractMockServerSpec.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/AbstractMockServerSpec.java
@@ -87,7 +87,7 @@ abstract class AbstractMockServerSpec<B extends WebTestClient.MockServerSpec<B>>
 		if (!CollectionUtils.isEmpty(this.filters)) {
 			builder.filters(theFilters -> theFilters.addAll(0, this.filters));
 		}
-		if (this.sessionManager != null) {
+		if (!builder.hasSessionManager() && this.sessionManager != null) {
 			builder.sessionManager(this.sessionManager);
 		}
 		if (!CollectionUtils.isEmpty(this.configurers)) {
diff --git a/spring-test/src/test/java/org/springframework/test/web/reactive/server/ApplicationContextSpecTests.java b/spring-test/src/test/java/org/springframework/test/web/reactive/server/ApplicationContextSpecTests.java
new file mode 100644
index 0000000000..5451d9ea3e
--- /dev/null
+++ b/spring-test/src/test/java/org/springframework/test/web/reactive/server/ApplicationContextSpecTests.java
@@ -0,0 +1,76 @@
+/*
+ * Copyright 2002-2018 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
+ *
+ *      http://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.test.web.reactive.server;
+
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.mock.web.server.MockWebSession;
+import org.springframework.web.reactive.config.EnableWebFlux;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.RouterFunctions;
+import org.springframework.web.reactive.function.server.ServerResponse;
+import org.springframework.web.server.session.WebSessionManager;
+
+/**
+ * Unit tests with {@link ApplicationContextSpec}.
+ * @author Rossen Stoyanchev
+ */
+public class ApplicationContextSpecTests {
+
+
+	@Test // SPR-17094
+	public void sessionManagerBean() {
+		ApplicationContext context = new AnnotationConfigApplicationContext(WebConfig.class);
+		ApplicationContextSpec spec = new ApplicationContextSpec(context);
+		WebTestClient testClient = spec.configureClient().build();
+
+		for (int i=0; i < 2; i++) {
+			testClient.get().uri("/sessionClassName")
+					.exchange()
+					.expectStatus().isOk()
+					.expectBody(String.class).isEqualTo("MockWebSession");
+		}
+	}
+
+
+	@Configuration
+	@EnableWebFlux
+	static class WebConfig {
+
+		@Bean
+		public RouterFunction<?> handler() {
+			return RouterFunctions.route()
+					.GET("/sessionClassName", request ->
+							request.session().flatMap(session -> {
+								String className = session.getClass().getSimpleName();
+								return ServerResponse.ok().syncBody(className);
+							}))
+					.build();
+		}
+
+		@Bean
+		public WebSessionManager webSessionManager() {
+			MockWebSession session = new MockWebSession();
+			return exchange -> Mono.just(session);
+		}
+	}
+
+}
diff --git a/spring-web/src/main/java/org/springframework/web/server/adapter/WebHttpHandlerBuilder.java b/spring-web/src/main/java/org/springframework/web/server/adapter/WebHttpHandlerBuilder.java
index 11fc8bde8e..d5fd97b78d 100644
--- a/spring-web/src/main/java/org/springframework/web/server/adapter/WebHttpHandlerBuilder.java
+++ b/spring-web/src/main/java/org/springframework/web/server/adapter/WebHttpHandlerBuilder.java
@@ -240,8 +240,17 @@ public final class WebHttpHandlerBuilder {
 	}
 
 	/**
-	 * Configure the {@link ServerCodecConfigurer} to set on the
-	 * {@link ServerWebExchange WebServerExchange}.
+	 * Whether a {@code WebSessionManager} is configured or not, either
+	 * detected from an {@code ApplicationContext} or explicitly configured via
+	 * {@link #sessionManager(WebSessionManager)}.
+	 * @since 5.0.9
+	 */
+	public boolean hasSessionManager() {
+		return this.sessionManager != null;
+	}
+
+	/**
+	 * Configure the {@link ServerCodecConfigurer} to set on the {@code WebServerExchange}.
 	 * @param codecConfigurer the codec configurer
 	 */
 	public WebHttpHandlerBuilder codecConfigurer(ServerCodecConfigurer codecConfigurer) {
@@ -249,6 +258,17 @@ public final class WebHttpHandlerBuilder {
 		return this;
 	}
 
+
+	/**
+	 * Whether a {@code ServerCodecConfigurer} is configured or not, either
+	 * detected from an {@code ApplicationContext} or explicitly configured via
+	 * {@link #codecConfigurer(ServerCodecConfigurer)}.
+	 * @since 5.0.9
+	 */
+	public boolean hasCodecConfigurer() {
+		return this.codecConfigurer != null;
+	}
+
 	/**
 	 * Configure the {@link LocaleContextResolver} to set on the
 	 * {@link ServerWebExchange WebServerExchange}.
@@ -259,6 +279,16 @@ public final class WebHttpHandlerBuilder {
 		return this;
 	}
 
+	/**
+	 * Whether a {@code LocaleContextResolver} is configured or not, either
+	 * detected from an {@code ApplicationContext} or explicitly configured via
+	 * {@link #localeContextResolver(LocaleContextResolver)}.
+	 * @since 5.0.9
+	 */
+	public boolean hasLocaleContextResolver() {
+		return this.localeContextResolver != null;
+	}
+
 
 	/**
 	 * Build the {@link HttpHandler}.