TEST BUG: MergeSchedulerSettingsTests fails always on small machines (o…

…pensearch-project#559)

MergeSchedulerSettingsTests tweaks the `node.processors` setting: sets it
explicitly to values of `2` and `8`. On a machine with only `4` threads
(e.g. my 2-core thinkpad), the test fails, because it creates unexpected
warnings about `node.processors` being set higher than the number of
cpus.

The problem can be reproduced always, by pretending to be single core:
```
./gradlew ':server:test' --tests "org.opensearch.index.MergeSchedulerSettingsTests.testMaxThreadAndMergeCount" -Dtests.jvm.argline="-XX:ActiveProcessorCount=1"
```

Instead, allow the test to provoke these specific warnings.

Signed-off-by: Robert Muir <rmuir@apache.org>

server/src/test/java/org/opensearch/index/MergeSchedulerSettingsTests.java

@@ -192,5 +192,14 @@ public void testMaxThreadAndMergeCount() {
         exc = expectThrows(IllegalArgumentException.class,
             () -> finalSettings.updateIndexMetadata(createMetadata(-1, 3, 8)));
         assertThat(exc.getMessage(), containsString("maxThreadCount (= 4) should be <= maxMergeCount (= 3)"));
+
+        // assertions above may provoke warnings if node.processors exceeds numCpus
+        // we explicitly test with values of 2 and 8
+        int numCpus = Runtime.getRuntime().availableProcessors();
+        String[] warnings = new String[] {
+            "setting [node.processors] to value [2] which is more than available processors [" + numCpus + "] is deprecated",
+            "setting [node.processors] to value [8] which is more than available processors [" + numCpus + "] is deprecated"
+        };
+        allowedWarnings(warnings);
     }
 }