Add AssertAllTest and update FileFilterTest

A new test class, AssertAllTest, has been added for testing the "Book" record functionalities. This includes tests for valid books using ISBN and invalid ISBNs. Moreover, unneeded import 'FilenameFilter' has been removed from the FileFilterTest class.

src/test/java/lambdas/AssertAllTest.java

@@ -0,0 +1,38 @@
+package lambdas;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class AssertAllTest {
+
+    // A record is an immutable data holder
+    // - autogenerates equals(), hashCode(), and toString()
+    // - primary or "canonical" constructor goes before the braces {}
+    // - "getter" methods match the names of the record components, e.g., title(), author(), year()
+    record Book(String title, String author, int year) {}
+
+    private Book findByIsbn(String isbn) {
+        if (!isbn.equals("978-0134685991")) {
+            throw new IllegalArgumentException("Unknown ISBN: " + isbn);
+        }
+        return new Book("Effective Java", "Joshua Bloch", 2008);
+    }
+
+    @Test
+    public void testBook() {
+        Book book = findByIsbn("978-0134685991");
+        assertAll(
+            () -> assertEquals("Effective Java", book.title()),
+            () -> assertEquals("Joshua Bloch", book.author()),
+            () -> assertEquals(2008, book.year())
+        );
+    }
+
+    @Test
+    void testInvalidIsbn() {
+        IllegalArgumentException exception = assertThrows(
+                IllegalArgumentException.class, () -> findByIsbn("123"));
+        assertEquals("Unknown ISBN: 123", exception.getMessage());
+    }
+}

src/test/java/lambdas/FileFilterTest.java

@@ -4,7 +4,6 @@
 
 import java.io.File;
 import java.io.FileFilter;
-import java.io.FilenameFilter;
 import java.util.List;
 import java.util.Map;