An incomplete shard snapshot will prevent a shard from moving away from a node (see `SnapshotInProgressAllocationDecider`). That means that when a shard snapshot completes it may become possible to perform some shard movements that previously were not possible, so we should trigger a reroute to start those movements. AFAICT we do not trigger such a reroute today.
test/framework/src/main/java/org/elasticsearch/test/ESTestCase.java
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.time.DateUtils;
import org.elasticsearch.common.time.FormatNames;
import org.elasticsearch.common.transport.TransportAddress;
import org.elasticsearch.common.unit.ByteSizeValue;
import org.elasticsearch.common.util.CollectionUtils;
import org.elasticsearch.common.util.Maps;
import org.elasticsearch.common.util.MockBigArrays;
import org.elasticsearch.common.util.concurrent.ThreadContext;
import org.elasticsearch.common.xcontent.LoggingDeprecationHandler;
import org.elasticsearch.common.xcontent.XContentHelper;
import org.elasticsearch.core.CheckedRunnable;
import org.elasticsearch.core.PathUtils;
import org.elasticsearch.core.PathUtilsForTesting;
import org.elasticsearch.core.RestApiVersion;
import org.elasticsearch.core.Strings;
import org.elasticsearch.core.SuppressForbidden;
import org.elasticsearch.core.Tuple;
import org.elasticsearch.env.Environment;
import org.elasticsearch.env.NodeEnvironment;
import org.elasticsearch.env.TestEnvironment;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexService.IndexCreationContext;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.IndexVersion;
import org.elasticsearch.index.analysis.AnalysisRegistry;
import org.elasticsearch.index.analysis.CharFilterFactory;
import org.elasticsearch.index.analysis.IndexAnalyzers;
import org.elasticsearch.index.analysis.TokenFilterFactory;
import org.elasticsearch.index.analysis.TokenizerFactory;