From 8dc0e9745ebe5ef65603868f190d520e59245f75 Mon Sep 17 00:00:00 2001
From: Ken Kousen <ken.kousen@kousenit.com>
Date: Wed, 21 Aug 2024 12:16:35 -0400
Subject: [PATCH] Add unit tests for FileFilter functionality

This commit introduces tests for various ways of filtering files in a directory using FileFilter and FilenameFilter. It covers anonymous inner classes, lambda expressions, method references, and assigned variable approaches. Additionally, it adds tests for listing java source files specifically.
---
 src/test/java/lambdas/FileFilterTest.java | 81 +++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 src/test/java/lambdas/FileFilterTest.java

diff --git a/src/test/java/lambdas/FileFilterTest.java b/src/test/java/lambdas/FileFilterTest.java
new file mode 100644
index 0000000..1d70bfd
--- /dev/null
+++ b/src/test/java/lambdas/FileFilterTest.java
@@ -0,0 +1,81 @@
+package lambdas;
+
+import org.junit.jupiter.api.DisplayNameGeneration;
+import org.junit.jupiter.api.DisplayNameGenerator;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.FileFilter;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@SuppressWarnings({"Convert2MethodRef", "Convert2Lambda", "Anonymous2MethodRef"})
+@DisplayNameGeneration(DisplayNameGenerator.ReplaceUnderscores.class)
+public class FileFilterTest {
+    private final File root = new File("src/main/java");
+
+    @Test
+    public void listFiles() {
+        File[] files = root.listFiles();
+        assert files != null;
+        assertEquals(22, files.length);
+    }
+
+    @Test
+    void listDirectories_anon_inner_class() {
+        File[] directories = root.listFiles(new FileFilter() {
+            @Override
+            public boolean accept(File pathname) {
+                return pathname.isDirectory();
+            }
+        });
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
+    @Test
+    void listDirectories_expression_lambda() {
+        File[] directories = root.listFiles(pathname -> pathname.isDirectory());
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
+    @Test
+    void listDirectories_method_reference() {
+        File[] directories = root.listFiles(File::isDirectory);
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
+    @Test
+    void listDirectories_block_lambda() {
+        File[] directories = root.listFiles(pathname -> {
+            System.out.println("Checking " + pathname.getName());
+            return pathname.isDirectory();
+        });
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
+    @Test
+    void listDirectories_assigned_variable() {
+        FileFilter filter = pathname -> pathname.isDirectory();
+        File[] directories = root.listFiles(filter);
+        assert directories != null;
+        assertEquals(14, directories.length);
+    }
+
+    @Test
+    void list_java_src_files_fileFilter() {
+        File[] javaFiles = root.listFiles(pathname -> pathname.getName().endsWith(".java"));
+        assert javaFiles != null;
+        assertEquals(8, javaFiles.length);
+    }
+
+    @Test
+    void list_java_src_files_filenameFilter() {
+        File[] javaFiles = root.listFiles((dir, name) -> name.endsWith(".java"));
+        assert javaFiles != null;
+        assertEquals(8, javaFiles.length);
+    }
+}