Remove reliance on side-effects in LogbackLoggingSystemTests

Closes gh-16160

spring-boot/src/test/java/org/springframework/boot/logging/logback/LogbackLoggingSystemTests.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -128,8 +128,9 @@ public class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 	}
 
 	@Test
-	public void testBasicConfigLocation() throws Exception {
+	public void defaultConfigConfiguresAConsoleAppender() throws Exception {
 		this.loggingSystem.beforeInitialize();
+		this.loggingSystem.initialize(this.initializationContext, null, null);
 		ILoggerFactory factory = StaticLoggerBinder.getSingleton().getLoggerFactory();
 		LoggerContext context = (LoggerContext) factory;
 		Logger root = context.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);