Add test for initialFileTime returning rounded millis

Author: kelunik

log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/RollingFileManagerTest.java

@@ -227,12 +227,17 @@ void testRolloverOfDeletedFile() throws IOException {
 
     @Test
     @Issue("https://github.com/apache/logging-log4j2/issues/3068")
-    void testInitialTimeRounded() {
+    void testInitialTimeRounded() throws IOException {
         assertEquals(1755031147000L, RollingFileManager.roundMillis(1755031147000L));
         assertEquals(1755031147000L, RollingFileManager.roundMillis(1755031147123L));
         assertEquals(1755031147000L, RollingFileManager.roundMillis(1755031147499L));
         assertEquals(1755031148000L, RollingFileManager.roundMillis(1755031147500L));
         assertEquals(1755031148000L, RollingFileManager.roundMillis(1755031147999L));
         assertEquals(1755031148000L, RollingFileManager.roundMillis(1755031148000L));
+
+        final File file = File.createTempFile("testFile", "log");
+        file.deleteOnExit();
+
+        assertEquals(0, RollingFileManager.initialFileTime(file) % 1000);
     }
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/appender/rolling/RollingFileManager.java

@@ -910,7 +910,7 @@ public RollingFileManager createManager(final String name, final FactoryData dat
         }
     }
 
-    private static long initialFileTime(final File file) {
+    static long initialFileTime(final File file) {
         final Path path = file.toPath();
         if (Files.exists(path)) {
             try {