Refactor FileFilterTest and add LazySupplierTest

Updated the FileFilterTest.java by revising existing tests and adding new ones for improved code coverage. The refactoring increases the usage of lambda expressions and method references for readability and conciseness. Simultaneously, a new test class LazySupplierTest.java has been added, which includes tests for both eager and lazy suppliers.

src/test/java/lambdas/FileFilterTest.java

@@ -4,6 +4,8 @@
 
 import java.io.File;
 import java.io.FileFilter;
+import java.util.List;
+import java.util.Map;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
@@ -36,6 +38,13 @@ void listDirectories_expressionLambda() {
         assertEquals(14, directories.length);
     }
 
+    @Test
+    void listDirectories_methodReference() {
+        File[] directories = root.listFiles(File::isDirectory);
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
     @Test
     void listDirectories_blockLambda() {
         File[] directories = root.listFiles(file -> {
@@ -48,17 +57,39 @@ void listDirectories_blockLambda() {
 
     @Test
     void listDirectories_fileFilterVariable() {
-        FileFilter filter = (File file) -> file.isDirectory();
+        FileFilter filter = File::isDirectory;
         File[] directories = root.listFiles(filter);
         assert directories != null;
         assertEquals(14, directories.length);
     }
 
     @Test
-    void listJavaSourceFiles() {
+    void listJavaSourceFiles_fileNameFilter() {
         // FilenameFilter filenameFilter = (File dir, String name) -> name.endsWith(".java");
         File[] javaFiles = root.listFiles((dir, name) -> name.endsWith(".java"));
         assert javaFiles != null;
         assertEquals(8, javaFiles.length);
     }
+
+    @Test
+    void listJavaSourceFiles_fileFilter() {
+        File[] javaFiles = root.listFiles(file -> file.getName().endsWith("."));
+        assert javaFiles != null;
+        assertEquals(8, javaFiles.length);
+    }
+
+    @Test
+    void forEachList() {
+        List<String> strings = List.of("this", "is", "a", "list", "of", "strings");
+        // for-each loop
+        for (String string : strings) {
+            System.out.println(string);
+        }
+
+        // forEach method in Iterable
+        strings.forEach(string -> System.out.println(string));
+
+        Map.of("a", 1, "b", 2, "c", 2)
+                .forEach((key, value) -> System.out.println(key + " = " + value));
+    }
 }

src/test/java/lambdas/LazySupplierTest.java

@@ -0,0 +1,35 @@
+package lambdas;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.logging.Logger;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class LazySupplierTest {
+    private final Logger logger = Logger.getLogger(LazySupplierTest.class.getName());
+
+    private String getErrorMessage() {
+        System.out.println("getErrorMessage() called");
+        return "Error message";
+    }
+
+    private String getLogMessage() {
+        System.out.println("getLogMessage() called");
+        return "Test passed";
+    }
+
+    @Test
+    void eagerSupplier() {
+        boolean x = true;
+        assertTrue(x, getErrorMessage());
+        logger.fine(getLogMessage());
+    }
+
+    @Test
+    void lazySupplier() {
+        boolean x = true;
+        assertTrue(x, () -> getErrorMessage());
+        logger.fine(() -> getLogMessage());
+    }
+}