Set watermarks in single-node test cases

We set the watermarks to low values in other test cases to prevent test
failures on nodes with low disk space (if the disk space is too low, the
test will fail anyway but we should not prematurely fail). This commit
sets the watermarks in the single-node test cases to avoid test failures
in such situations.

Relates #28134

Author: jasontedor

test/framework/src/main/java/org/elasticsearch/test/ESSingleNodeTestCase.java

@@ -29,6 +29,7 @@
 import org.elasticsearch.cluster.health.ClusterHealthStatus;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
+import org.elasticsearch.cluster.routing.allocation.DiskThresholdSettings;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.network.NetworkModule;
 import org.elasticsearch.common.settings.Settings;
@@ -176,6 +177,9 @@ private Node newNode() {
             .put("transport.type", "local")
             .put(Node.NODE_DATA_SETTING.getKey(), true)
             .put(NodeEnvironment.NODE_ID_SEED_SETTING.getKey(), random().nextLong())
+            // default the watermarks low values to prevent tests from failing on nodes without enough disk space
+            .put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK_SETTING.getKey(), "1b")
+            .put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK_SETTING.getKey(), "1b")
             .put(nodeSettings()) // allow test cases to provide their own settings or override these
             .build();
         Collection<Class<? extends Plugin>> plugins = getPlugins();