Add FileFilter tests and simplify stream collection usage

Introduce new unit tests in `FileFilterTest.java` to demonstrate various file filtering and iteration approaches using lambdas and method references. Additionally, refactor `AntarcticaTimeZones.java` to use the simplified `toList()` method for stream collection, enhancing code readability.

src/main/java/datetime/AntarcticaTimeZones.java

@@ -18,7 +18,7 @@ public static void main(String[] args) {
                         .map(now::atZone) // Stream<ZonedDateTime>
                         .sorted(comparingInt(
                                 zoneId -> zoneId.getOffset().getTotalSeconds()))
-                        .collect(Collectors.toList());
+                        .toList();
 
         antarcticZones.forEach(zdt ->
                 System.out.printf("UTC%6s: %25s %7s%n", zdt.getOffset(), zdt.getZone(),

src/test/java/lambdas/FileFilterTest.java

@@ -0,0 +1,79 @@
+package lambdas;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.FileFilter;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class FileFilterTest {
+    private final File root = new File("src");
+
+    @Test
+    void listFiles() {
+        File[] files = root.listFiles();
+        assert files != null;
+        for (File file : files) {
+            System.out.println(file);
+        }
+    }
+
+    @Test
+    void listDirectories_fileFilter_anoninnerclass() {
+        File[] files = root.listFiles(new FileFilter() {
+            @Override
+            public boolean accept(File pathname) {
+                return pathname.isDirectory();
+            }
+        });
+        assert files != null;
+        for (File file : files) {
+            System.out.println(file);
+        }
+    }
+
+    @Test
+    void listDirectories_fileFilter_expressionlambda() {
+        File[] files = root.listFiles(pathname -> pathname.isDirectory());
+        assert files != null;
+        assertEquals(2, files.length);
+    }
+
+    @Test
+    void listDirectories_fileNameFilter_expressionlambda() {
+        File[] files = root.listFiles((dir, name) -> new File(dir, name).isDirectory());
+        assert files != null;
+        assertEquals(2, files.length);
+    }
+
+    @Test
+    void listDirectories_fileFilter_variable() {
+        FileFilter fileFilter = (File pathname) -> pathname.isDirectory();
+        File[] files = root.listFiles(fileFilter);
+        assert files != null;
+        assertEquals(2, files.length);
+    }
+
+    @Test
+    void listDirectories_fileFilter_methodReference() {
+        File[] files = root.listFiles(File::isDirectory);
+        assert files != null;
+        assertEquals(2, files.length);
+    }
+
+    @Test
+    void iterateOverMap() {
+        Map.of("a", 1, "b", 2, "c", 2)
+                .forEach((k, v) -> System.out.println(k + " -> " + v));
+    }
+
+    @Test
+    void iterateOverList() {
+        List.of("this", "is", "a", "list")
+                .forEach(System.out::println);
+
+    }
+}