Fix ILMHistoryItemTests.testTruncateLongError (elastic#125814)

It should work independent of how many characters are truncated now.

Resolves elastic#125216

Author: dakrone

muted-tests.yml

@@ -338,9 +338,6 @@ tests:
 - class: org.elasticsearch.index.engine.ThreadPoolMergeSchedulerTests
   method: testSchedulerCloseWaitsForRunningMerge
   issue: https://github.com/elastic/elasticsearch/issues/125236
-- class: org.elasticsearch.xpack.ilm.history.ILMHistoryItemTests
-  method: testTruncateLongError
-  issue: https://github.com/elastic/elasticsearch/issues/125216
 - class: org.elasticsearch.index.shard.StoreRecoveryTests
   method: testAddIndices
   issue: https://github.com/elastic/elasticsearch/issues/124104

x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/ilm/history/ILMHistoryItemTests.java

@@ -22,7 +22,9 @@
 import java.util.Map;
 
 import static org.elasticsearch.xcontent.XContentFactory.jsonBuilder;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.matchesPattern;
 import static org.hamcrest.Matchers.startsWith;
 
 public class ILMHistoryItemTests extends ESTestCase {
@@ -135,15 +137,15 @@ public void testTruncateLongError() throws IOException {
             try (XContentParser p = XContentFactory.xContent(XContentType.JSON).createParser(XContentParserConfiguration.EMPTY, json)) {
                 Map<String, Object> item = p.map();
                 assertThat(
-                    item.get("error_details"),
-                    equalTo(
+                    (String) item.get("error_details"),
+                    containsString(
                         "{\"type\":\"illegal_argument_exception\",\"reason\":\""
                             // We subtract a number of characters here due to the truncation being based
                             // on the length of the whole string, not just the "reason" part.
                             + longError.substring(0, LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH - 47)
-                            + "... (5126 chars truncated)\"}"
                     )
                 );
+                assertThat((String) item.get("error_details"), matchesPattern(".*\\.\\.\\. \\(\\d+ chars truncated\\).*"));
             }
         }
     }