Fix off-by-one error in an index shard test

There is an off-by-one error in this test. It leads to the recovery
thread never being started, and that means joining on it will wait
indefinitely. This commit addresses that by fixing the off-by-one error.

Relates #42325

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -1732,12 +1732,11 @@ public void testDelayedOperationsBeforeAndAfterRelocated() throws Exception {
         recoveryThread.start();
 
         final int numberOfAcquisitions = randomIntBetween(1, 10);
-        final int recoveryIndex = randomIntBetween(1, numberOfAcquisitions);
+        final List<Runnable> assertions = new ArrayList<>(numberOfAcquisitions);
+        final int recoveryIndex = randomIntBetween(0, numberOfAcquisitions - 1);
 
         for (int i = 0; i < numberOfAcquisitions; i++) {
-
             final PlainActionFuture<Releasable> onLockAcquired;
-            final Runnable assertion;
             if (i < recoveryIndex) {
                 final AtomicBoolean invoked = new AtomicBoolean();
                 onLockAcquired = new PlainActionFuture<Releasable>() {
@@ -1755,26 +1754,29 @@ public void onFailure(Exception e) {
                     }
 
                 };
-                assertion = () -> assertTrue(invoked.get());
+                assertions.add(() -> assertTrue(invoked.get()));
             } else if (recoveryIndex == i) {
                 startRecovery.countDown();
                 relocationStarted.await();
                 onLockAcquired = new PlainActionFuture<>();
-                assertion = () -> {
+                assertions.add(() -> {
                     final ExecutionException e = expectThrows(ExecutionException.class, () -> onLockAcquired.get(30, TimeUnit.SECONDS));
                     assertThat(e.getCause(), instanceOf(ShardNotInPrimaryModeException.class));
                     assertThat(e.getCause(), hasToString(containsString("shard is not in primary mode")));
-                };
+                });
             } else {
                 onLockAcquired = new PlainActionFuture<>();
-                assertion = () -> {
+                assertions.add(() -> {
                     final ExecutionException e = expectThrows(ExecutionException.class, () -> onLockAcquired.get(30, TimeUnit.SECONDS));
                     assertThat(e.getCause(), instanceOf(ShardNotInPrimaryModeException.class));
                     assertThat(e.getCause(), hasToString(containsString("shard is not in primary mode")));
-                };
+                });
             }
 
             shard.acquirePrimaryOperationPermit(onLockAcquired, ThreadPool.Names.WRITE, "i_" + i);
+        }
+
+        for (final Runnable assertion : assertions) {
             assertion.run();
         }