feature: Rewrite thread-local storage pattern (#2452)

thread-local-storage/src/test/java/ThreadLocalTest.java

@@ -0,0 +1,68 @@
+import com.iluwatar.WithThreadLocal;
+import com.iluwatar.WithoutThreadLocal;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class ThreadLocalTest {
+
+    private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+    private final PrintStream originalOut = System.out;
+
+    @BeforeEach
+    public void setUpStreams() {
+        System.setOut(new PrintStream(outContent));
+    }
+
+    @AfterEach
+    public void restoreStreams() {
+        System.setOut(originalOut);
+    }
+
+    @Test
+    public void withoutThreadLocal() throws InterruptedException {
+        int initialValue = 1234567890;
+
+        int threadSize = 2;
+        ExecutorService executor = Executors.newFixedThreadPool(threadSize);
+
+        WithoutThreadLocal threadLocal = new WithoutThreadLocal(initialValue);
+        for (int i = 0; i < threadSize; i++) {
+            executor.submit(threadLocal);
+        }
+        executor.awaitTermination(3, TimeUnit.SECONDS);
+
+        List<String> lines = outContent.toString().lines().toList();
+        //Matches only first thread, the second has changed by first thread value
+        Assertions.assertFalse(lines.stream()
+                .allMatch(line -> line.endsWith(String.valueOf(initialValue))));
+    }
+
+    @Test
+    public void withThreadLocal() throws InterruptedException {
+        int initialValue = 1234567890;
+
+        int threadSize = 2;
+        ExecutorService executor = Executors.newFixedThreadPool(threadSize);
+
+        WithThreadLocal threadLocal = new WithThreadLocal(ThreadLocal.withInitial(() -> initialValue));
+        for (int i = 0; i < threadSize; i++) {
+            executor.submit(threadLocal);
+        }
+
+        executor.awaitTermination(3, TimeUnit.SECONDS);
+        threadLocal.remove();
+
+        List<String> lines = outContent.toString().lines().toList();
+        Assertions.assertTrue(lines.stream()
+                .allMatch(line -> line.endsWith(String.valueOf(initialValue))));
+    }
+}