Fix UtilsTest, create MessageKeyTest

src/test/java/fr/xephi/authme/settings/MessageKeyTest.java

@@ -0,0 +1,33 @@
+package fr.xephi.authme.settings;
+
+import fr.xephi.authme.util.StringUtils;
+import org.junit.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.junit.Assert.fail;
+
+/**
+ * Test for {@link MessageKey}.
+ */
+public class MessageKeyTest {
+
+    @Test
+    public void shouldHaveUniqueMessageKeys() {
+        // given
+        MessageKey[] messageKeys = MessageKey.values();
+        Set<String> keys = new HashSet<>();
+
+        // when / then
+        for (MessageKey messageKey : messageKeys) {
+            String key = messageKey.getKey();
+            if (keys.contains(key)) {
+                fail("Found key '" + messageKey.getKey() + "' twice!");
+            } else if (StringUtils.isEmpty(key)) {
+                fail("Key for message key '" + messageKey + "' is empty");
+            }
+            keys.add(key);
+        }
+    }
+}