Suppress debug log output during Logback initialization

Closes gh-11761

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -111,8 +111,8 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		if (isAlreadyInitialized(loggerContext)) {
 			return;
 		}
-		loggerContext.getTurboFilterList().remove(FILTER);
 		super.initialize(initializationContext, configLocation, logFile);
+		loggerContext.getTurboFilterList().remove(FILTER);
 		markAsInitialized(loggerContext);
 		if (StringUtils.hasText(System.getProperty(CONFIGURATION_FILE_PROPERTY))) {
 			getLogger(LogbackLoggingSystem.class.getName()).warn(

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

@@ -39,6 +39,7 @@ import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
+import org.junit.runner.RunWith;
 import org.slf4j.ILoggerFactory;
 import org.slf4j.bridge.SLF4JBridgeHandler;
 import org.slf4j.impl.StaticLoggerBinder;
@@ -52,6 +53,8 @@ import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.LoggingSystemProperties;
 import org.springframework.boot.testsupport.assertj.Matched;
 import org.springframework.boot.testsupport.rule.OutputCapture;
+import org.springframework.boot.testsupport.runner.classpath.ClassPathExclusions;
+import org.springframework.boot.testsupport.runner.classpath.ModifiedClassPathRunner;
 import org.springframework.mock.env.MockEnvironment;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.util.FileCopyUtils;
@@ -74,6 +77,8 @@ import static org.mockito.Mockito.verify;
  * @author Madhura Bhave
  * @author Vedran Pavic
  */
+@RunWith(ModifiedClassPathRunner.class)
+@ClassPathExclusions("log4j-*.jar")
 public class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 
 	@Rule
@@ -141,12 +146,14 @@ public class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 
 	@Test
 	public void testNonDefaultConfigLocation() {
+		int existingOutputLength = this.output.toString().length();
 		this.loggingSystem.beforeInitialize();
 		this.loggingSystem.initialize(this.initializationContext,
 				"classpath:logback-nondefault.xml",
 				getLogFile(tmpDir() + "/tmp.log", null));
 		this.logger.info("Hello world");
 		String output = this.output.toString().trim();
+		assertThat(output.substring(existingOutputLength)).doesNotContain("DEBUG");
 		assertThat(output).contains("Hello world").contains(tmpDir() + "/tmp.log");
 		assertThat(output).endsWith("BOOTBOOT");
 		assertThat(new File(tmpDir() + "/tmp.log").exists()).isFalse();