[TEST] guarantee REST tests execution order

REST tests are being shuffled before their execution. To guarantee their repeatability given the seed, their order needs to be always the same before the shuffling happens.

Closes #8745

src/test/java/org/elasticsearch/test/rest/ElasticsearchRestTests.java

@@ -49,9 +49,7 @@ import java.io.IOException;
 import java.nio.file.FileSystems;
 import java.nio.file.PathMatcher;
 import java.nio.file.Paths;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
+import java.util.*;
 
 /**
  * Runs the clients test suite against an elasticsearch cluster.
@@ -133,12 +131,10 @@ public class ElasticsearchRestTests extends ElasticsearchIntegrationTest {
         String[] paths = resolvePathsProperty(REST_TESTS_SUITE, DEFAULT_TESTS_PATH);
         Map<String, Set<File>> yamlSuites = FileUtils.findYamlSuites(DEFAULT_TESTS_PATH, paths);
 
-        //yaml suites are grouped by directory (effectively by api)
-        List<String> apis = Lists.newArrayList(yamlSuites.keySet());
-
         List<RestTestCandidate> testCandidates = Lists.newArrayList();
         RestTestSuiteParser restTestSuiteParser = new RestTestSuiteParser();
-        for (String api : apis) {
+        //yaml suites are grouped by directory (effectively by api)
+        for (String api : yamlSuites.keySet()) {
             List<File> yamlFiles = Lists.newArrayList(yamlSuites.get(api));
             for (File yamlFile : yamlFiles) {
                 //tests distribution disabled for now since it causes reporting problems,
@@ -151,6 +147,15 @@ public class ElasticsearchRestTests extends ElasticsearchIntegrationTest {
                 //}
             }
         }
+
+        //sort the candidates so they will always be in the same order before being shuffled, for repeatability
+        Collections.sort(testCandidates, new Comparator<RestTestCandidate>() {
+            @Override
+            public int compare(RestTestCandidate o1, RestTestCandidate o2) {
+                return o1.getTestPath().compareTo(o2.getTestPath());
+            }
+        });
+
         return testCandidates;
     }