Fix tests in SetSingleNodeAllocateStepTests (#135724)

By doing
`VersionUtils.randomCompatibleVersion(random(), VersionUtils.getPreviousVersion())`,
we could also get `Version.CURRENT`, as that version is also compatible
with the previous version (unless we're running right after a major
version was released). If the `oldVersion` variable in these tests is
equal to the current version, the tests will fail as their whole goal is
to verify behavior with different node versions. Instead, we should get a
random version that is at most the previous version, to guarantee that
`oldVersion` always precedes the current version.

Fixes #135590

Author: nielsbauman

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ilm/SetSingleNodeAllocateStepTests.java

@@ -29,6 +29,7 @@
 import org.elasticsearch.common.settings.Settings.Builder;
 import org.elasticsearch.common.transport.TransportAddress;
 import org.elasticsearch.common.util.Maps;
+import org.elasticsearch.env.BuildVersion;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexNotFoundException;
 import org.elasticsearch.index.IndexVersion;
@@ -394,11 +395,7 @@ public void testPerformActionAttrsNoShard() {
     }
 
     public void testPerformActionSomeShardsOnlyOnNewNodes() throws Exception {
-        VersionInformation oldVersion = new VersionInformation(
-            VersionUtils.randomCompatibleVersion(random(), VersionUtils.getPreviousVersion()),
-            IndexVersions.MINIMUM_COMPATIBLE,
-            IndexVersionUtils.randomCompatibleVersion(random())
-        );
+        final VersionInformation oldVersion = randomOldVersionInformation();
         final int numNodes = randomIntBetween(2, 20); // Need at least 2 nodes to have some nodes on a new version
         final int numNewNodes = randomIntBetween(1, numNodes - 1);
         final int numOldNodes = numNodes - numNewNodes;
@@ -459,11 +456,7 @@ public void testPerformActionSomeShardsOnlyOnNewNodes() throws Exception {
     }
 
     public void testPerformActionSomeShardsOnlyOnNewNodesButNewNodesInvalidAttrs() {
-        VersionInformation oldVersion = new VersionInformation(
-            VersionUtils.randomCompatibleVersion(random(), VersionUtils.getPreviousVersion()),
-            IndexVersions.MINIMUM_COMPATIBLE,
-            IndexVersionUtils.randomCompatibleVersion(random())
-        );
+        final var oldVersion = randomOldVersionInformation();
         final int numNodes = randomIntBetween(2, 20); // Need at least 2 nodes to have some nodes on a new version
         final int numNewNodes = randomIntBetween(1, numNodes - 1);
         final int numOldNodes = numNodes - numNewNodes;
@@ -532,11 +525,7 @@ public void testPerformActionSomeShardsOnlyOnNewNodesButNewNodesInvalidAttrs() {
     }
 
     public void testPerformActionNewShardsExistButWithInvalidAttributes() throws Exception {
-        VersionInformation oldVersion = new VersionInformation(
-            VersionUtils.randomCompatibleVersion(random(), VersionUtils.getPreviousVersion()),
-            IndexVersions.MINIMUM_COMPATIBLE,
-            IndexVersionUtils.randomCompatibleVersion(random())
-        );
+        final VersionInformation oldVersion = randomOldVersionInformation();
         final int numNodes = randomIntBetween(2, 20); // Need at least 2 nodes to have some nodes on a new version
         final int numNewNodes = randomIntBetween(1, numNodes - 1);
         final int numOldNodes = numNodes - numNewNodes;
@@ -604,6 +593,18 @@ public void testPerformActionNewShardsExistButWithInvalidAttributes() throws Exc
         assertNodeSelected(indexMetadata, indexMetadata.getIndex(), oldNodeIds, discoveryNodes, indexRoutingTable.build());
     }
 
+    private VersionInformation randomOldVersionInformation() {
+        final var previousVersion = VersionUtils.getPreviousVersion();
+        final var version = VersionUtils.randomVersionBetween(random(), previousVersion.minimumCompatibilityVersion(), previousVersion);
+        return new VersionInformation(
+            BuildVersion.fromVersionId(version.id()),
+            version,
+            IndexVersions.MINIMUM_COMPATIBLE,
+            IndexVersions.MINIMUM_COMPATIBLE,
+            IndexVersionUtils.randomCompatibleVersion(random())
+        );
+    }
+
     private Collection<Map.Entry<String, String>> generateRandomValidAttributes(int numAttrs) {
         return generateRandomValidAttributes(numAttrs, "");
     }