[TASK] Add a test about Unicode preservation

src/test/java/net/sourceforge/plantuml/servlet/TestCharset.java

+package net.sourceforge.plantuml.servlet;
+
+import com.meterware.httpunit.GetMethodWebRequest;
+import com.meterware.httpunit.WebConversation;
+import com.meterware.httpunit.WebRequest;
+import com.meterware.httpunit.WebResponse;
+
+public class TestCharset extends WebappTestCase {
+
+    /**
+     * Verifies the preservation of unicode characters for the "Bob -> Alice : hell‽" sample
+     */
+    public void testUnicodeSupport() throws Exception {
+        WebConversation conversation = new WebConversation();
+        WebRequest request = new GetMethodWebRequest(getServerUrl() + "txt/SyfFKj2rKt3CoKnELR1Io4ZDoNdKi1S0");
+        WebResponse response = conversation.getResource(request);
+        // Analyze response
+        // Verifies the Content-Type header
+        assertEquals("Response content type is not TEXT PLAIN", "text/plain", response.getContentType());
+        // Get the content and verify that the interrobang unicode character is present
+        String diagram = response.getText();
+        assertTrue("Interrobang unicode character is not preserved", diagram.contains("‽"));
+    }
+    
+    /**
+     * Verifies the preservation of unicode characters for the "participant Bob [[http://www.snow.com/❄]]\nBob -> Alice" sample
+     */
+    public void testUnicodeInCMap() throws Exception {
+        WebConversation conversation = new WebConversation();
+        WebRequest request = new GetMethodWebRequest(getServerUrl() + "map/AqWiAibCpYn8p2jHSCfFKeYEpYWfAR3IroylBzShpiilrqlEpzL_DBSbDfOB9Azhf-2OavcS2W00");
+        WebResponse response = conversation.getResource(request);
+        // Analyze response
+        // Verifies the Content-Type header
+        assertEquals("Response content type is not TEXT PLAIN", "text/plain", response.getContentType());
+        // Get the content and verify that the snow unicode character is present
+        String map = response.getText();
+        assertTrue("Snow unicode character is not preserved", map.contains("❄"));
+    }
+
+
+}