Bael 822 thread local (#1625)

* code for thread local article

* userNameSecret

* better to string

* fix typo

core-java/src/test/java/com/baeldung/threadlocal/ThreadLocalTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.threadlocal;
+
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutionException;
+
+import static org.junit.Assert.assertEquals;
+
+public class ThreadLocalTest {
+    @Test
+    public void givenThreadThatStoresContextInAMap_whenStartThread_thenShouldSetContextForBothUsers() throws ExecutionException, InterruptedException {
+        //when
+        SharedMapWithUserContext firstUser = new SharedMapWithUserContext(1);
+        SharedMapWithUserContext secondUser = new SharedMapWithUserContext(2);
+        new Thread(firstUser).start();
+        new Thread(secondUser).start();
+
+        Thread.sleep(3000);
+        //then
+        assertEquals(SharedMapWithUserContext.userContextPerUserId.size(), 2);
+    }
+
+    @Test
+    public void givenThreadThatStoresContextInThreadLocal_whenStartThread_thenShouldStoreContextInThreadLocal() throws ExecutionException, InterruptedException {
+        //when
+        ThreadLocalWithUserContext firstUser = new ThreadLocalWithUserContext(1);
+        ThreadLocalWithUserContext secondUser = new ThreadLocalWithUserContext(2);
+        new Thread(firstUser).start();
+        new Thread(secondUser).start();
+
+        Thread.sleep(3000);
+    }
+
+}