Change LoggingSystemTests to use real temp folder

Update AbstractLoggingSystemTests to use a TemporaryFolder rule.

Fixes gh-3349

spring-boot/src/test/java/org/springframework/boot/logging/AbstractLoggingSystemTests.java

@@ -16,16 +16,14 @@
 
 package org.springframework.boot.logging;
 
-import java.io.File;
+import java.io.IOException;
 
 import org.junit.After;
-import org.junit.AfterClass;
 import org.junit.Before;
-import org.junit.BeforeClass;
+import org.junit.Rule;
+import org.junit.rules.TemporaryFolder;
 import org.springframework.util.StringUtils;
 
-import static org.junit.Assert.assertTrue;
-
 /**
  * Base for {@link LoggingSystem} tests.
  *
@@ -36,31 +34,20 @@ public abstract class AbstractLoggingSystemTests {
 
 	private static final String JAVA_IO_TMPDIR = "java.io.tmpdir";
 
-	private static String tempDir;
-
-	@BeforeClass
-	public static void configureTempdir() {
-		tempDir = System.getProperty(JAVA_IO_TMPDIR);
-		File newTempDir = new File("target/tmp");
-		newTempDir.mkdirs();
-		System.setProperty(JAVA_IO_TMPDIR, newTempDir.getAbsolutePath());
-	}
+	@Rule
+	public TemporaryFolder temp = new TemporaryFolder();
 
-	@AfterClass
-	public static void reinstateTempDir() {
-		System.setProperty(JAVA_IO_TMPDIR, tempDir);
-	}
+	private String originalTempFolder;
 
 	@Before
-	public void deleteTempLog() {
-		deleteFile(new File(tmpDir() + "/spring.log"));
-		deleteFile(new File(tmpDir() + "/tmp.log"));
+	public void configureTempdir() throws IOException {
+		this.originalTempFolder = System.getProperty(JAVA_IO_TMPDIR);
+		System.setProperty(JAVA_IO_TMPDIR, this.temp.newFolder().getAbsolutePath());
 	}
 
-	private void deleteFile(File file) {
-		if (file.exists()) {
-			assertTrue("Unable to delete file", file.delete());
-		}
+	@After
+	public void reinstateTempDir() {
+		System.setProperty(JAVA_IO_TMPDIR, this.originalTempFolder);
 	}
 
 	@After