Make WebTestClient auto-config back off without CodecCustomizer

Fixes gh-46678

Author: wilkinsona

module/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/WebTestClientAutoConfiguration.java

@@ -44,7 +44,7 @@
  */
 @AutoConfiguration(afterName = { "org.springframework.boot.http.codec.autoconfigure.CodecsAutoConfiguration",
 		"org.springframework.boot.webflux.autoconfigure.WebFluxAutoConfiguration" })
-@ConditionalOnClass({ WebClient.class, WebTestClient.class })
+@ConditionalOnClass({ CodecCustomizer.class, WebClient.class, WebTestClient.class })
 @Import(WebTestClientSecurityConfiguration.class)
 @EnableConfigurationProperties
 public final class WebTestClientAutoConfiguration {

module/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/reactive/WebTestClientAutoConfigurationTests.java

@@ -119,6 +119,14 @@ void shouldNotApplySpringSecurityConfigurerWhenSpringSecurityNotOnClassPath() {
 			});
 	}
 
+	@Test
+	void shouldBackOffWithoutCodecCustomizer() {
+		FilteredClassLoader classLoader = new FilteredClassLoader(CodecCustomizer.class);
+		this.contextRunner.withUserConfiguration(BaseConfiguration.class)
+			.withClassLoader(classLoader)
+			.run((context) -> assertThat(context).doesNotHaveBean(WebTestClient.class));
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class BaseConfiguration {