#1467 Rearrange old keys migration so no entries get lost

- 'error' was an old entry but now we have multiple entries under 'error' (which is now a section), so we need to ensure that we migrate the old 'error' entry before the migration sets anything under that path

src/test/java/fr/xephi/authme/message/updater/MessageUpdaterTest.java

@@ -108,7 +108,7 @@ public class MessageUpdaterTest {
             .collect(Collectors.toSet());
 
         // when
-        Set<String> messageKeysFromConfigData = MessageUpdater.CONFIGURATION_DATA.getProperties().stream()
+        Set<String> messageKeysFromConfigData = MessageUpdater.getConfigurationData().getProperties().stream()
             .map(Property::getPath)
             .collect(Collectors.toSet());
 
@@ -125,7 +125,7 @@ public class MessageUpdaterTest {
 
         // when
         Map<String, String[]> comments = ReflectionTestUtils.getFieldValue(
-            ConfigurationData.class, MessageUpdater.CONFIGURATION_DATA, "sectionComments");
+            ConfigurationData.class, MessageUpdater.getConfigurationData(), "sectionComments");
 
         // then
         assertThat(comments.keySet(), equalTo(rootPaths));

src/test/java/fr/xephi/authme/message/updater/OldMessageKeysMigraterTest.java

@@ -0,0 +1,41 @@
+package fr.xephi.authme.message.updater;
+
+import fr.xephi.authme.message.MessageKey;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import static org.junit.Assert.fail;
+
+/**
+ * Test for {@link OldMessageKeysMigrater}.
+ */
+public class OldMessageKeysMigraterTest {
+
+    @Test
+    public void shouldHasOldKeysThatAreNewParentsFirstInMap() {
+        // given
+        Set<String> parentPaths = collectParentPathsFromMessageKeys();
+        Set<String> encounteredParents = new HashSet<>();
+
+        // when / then
+        for (Map.Entry<MessageKey, String> entry : OldMessageKeysMigrater.KEYS_TO_OLD_PATH.entrySet()) {
+            if (parentPaths.contains(entry.getValue()) && encounteredParents.contains(entry.getValue())) {
+                fail("Entry migrating old path '" + entry.getValue()
+                    + "' should come before any new paths with it as parent");
+            }
+            String parent = entry.getKey().getKey().split("\\.")[0];
+            encounteredParents.add(parent);
+        }
+    }
+
+    private Set<String> collectParentPathsFromMessageKeys() {
+        return Arrays.stream(MessageKey.values())
+            .map(mk -> mk.getKey().split("\\.")[0])
+            .collect(Collectors.toSet());
+    }
+}