add more usage examples

Signed-off-by: Ceki Gulcu <ceki@qos.ch>

slf4j-api/src/test/java/org/slf4j/MDCHelperTest.java

@@ -1,15 +1,72 @@
+/**
+ * Copyright (c) 2004-2023 QOS.ch
+ * All rights reserved.
+ * <p>
+ * Permission is hereby granted, free  of charge, to any person obtaining
+ * a  copy  of this  software  and  associated  documentation files  (the
+ * "Software"), to  deal in  the Software without  restriction, including
+ * without limitation  the rights to  use, copy, modify,  merge, publish,
+ * distribute,  sublicense, and/or sell  copies of  the Software,  and to
+ * permit persons to whom the Software  is furnished to do so, subject to
+ * the following conditions:
+ * <p>
+ * The  above  copyright  notice  and  this permission  notice  shall  be
+ * included in all copies or substantial portions of the Software.
+ * <p>
+ * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
+ * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
+ * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
 package org.slf4j;
 
 import org.junit.Test;
+import org.slf4j.helpers.BasicMDCAdapter;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 public class MDCHelperTest {
 
 
+    BasicMDCAdapter mdcAdapter = new BasicMDCAdapter();
+    MDCHelper mdch = new MDCHelper(mdcAdapter);
+
+    String k0 = "k0";
+    String v0 = "v0";
+    String kUnused = "kUnused";
+
+    void throwRuntimeException() {
+        throw new RuntimeException();
+    }
+
     @Test
     public void smoke() {
-        MDCHelper mdch = new MDCHelper();
-
-        //mdch.addKey()
+        try {
+            mdch.put(k0, v0);
+            assertEquals(v0, mdcAdapter.get(k0));
+            assertNull(mdcAdapter.get(kUnused));
+            throwRuntimeException();
+        } catch (RuntimeException e) {
+            assertEquals(v0, mdcAdapter.get(k0));
+        } finally {
+            mdch.removeSet();
+        }
+        assertNull(mdcAdapter.get(k0));
+    }
 
+    @Test
+    public void empty() {
+        try {
+            assertNull(mdcAdapter.get(kUnused));
+        } finally {
+            mdch.removeSet();
+        }
+        assertNull(mdcAdapter.get(k0));
     }
 }