Fix test bug in DynamicMappingsIT. (elastic#37906)

Closes elastic#37898

server/src/test/java/org/elasticsearch/index/mapper/DynamicMappingIT.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.InternalSettingsPlugin;
+import org.hamcrest.Matchers;
 
 import java.io.IOException;
 import java.util.Collection;
@@ -41,7 +42,6 @@ protected Collection<Class<? extends Plugin>> nodePlugins() {
         return Collections.singleton(InternalSettingsPlugin.class);
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/37898")
     public void testConflictingDynamicMappings() {
         // we don't use indexRandom because the order of requests is important here
         createIndex("index");
@@ -50,7 +50,15 @@ public void testConflictingDynamicMappings() {
             client().prepareIndex("index", "type", "2").setSource("foo", "bar").get();
             fail("Indexing request should have failed!");
         } catch (MapperParsingException e) {
-            // expected
+            // general case, the parsing code complains that it can't parse "bar" as a "long"
+            assertThat(e.getMessage(),
+                    Matchers.containsString("failed to parse field [foo] of type [long]"));
+        } catch (IllegalArgumentException e) {
+            // rare case: the node that processes the index request doesn't have the mappings
+            // yet and sends a mapping update to the master node to map "bar" as "text". This
+            // fails as it had been already mapped as a long by the previous index request.
+            assertThat(e.getMessage(),
+                    Matchers.containsString("mapper [foo] of different type, current_type [long], merged_type [text]"));
         }
     }