Add comment, simplify

Author: JeremyDahlgren

server/src/internalClusterTest/java/org/elasticsearch/snapshots/SnapshotShutdownIT.java

@@ -480,7 +480,7 @@ public void testShutdownWhileSuccessInFlight() throws Exception {
     )
     public void testSnapshotShutdownProgressTracker() throws Exception {
         final var repoName = randomIdentifier();
-        final int numShards = randomIntBetween(1, 10);
+        final int numShards = randomIntBetween(1, 9);
         createRepository(repoName, "mock");
 
         // Create another index on another node which will be blocked (remain in state INIT) throughout.
@@ -540,13 +540,14 @@ public void testSnapshotShutdownProgressTracker() throws Exception {
         mockLog.awaitAllExpectationsMatched();
         resetMockLog();
 
-        assert 1 <= numShards && numShards <= 10;
+        // At least one shard reached the MockRepository's blocking code when waitForBlock was called. However, there's no guarantee that
+        // the other shards got that far before the shutdown flag was put in place, in which case the other shards may be paused instead.
         mockLog.addExpectation(
             new MockLog.PatternSeenEventExpectation(
                 "SnapshotShutdownProgressTracker running number of snapshots",
                 SnapshotShutdownProgressTracker.class.getCanonicalName(),
                 Level.INFO,
-                ".+Number shard snapshots running \\[" + (numShards < 10 ? "[1-" + numShards + "]" : "([1-9]|10)") + "].+"
+                ".+Number shard snapshots running \\[[1-" + numShards + "]].+"
             )
         );