Support using a fake node count for unit tests

Allowing the LocalQueryRunner to estimate costs using a fake node count
allows unit tests to consider network costs and different cluster
configurations.

Author: rschlussel-zz

presto-main/src/main/java/com/facebook/presto/testing/LocalQueryRunner.java

@@ -251,15 +251,16 @@ public LocalQueryRunner(Session defaultSession)
                 new FeaturesConfig()
                         .setOptimizeMixedDistinctAggregations(true)
                         .setIterativeOptimizerEnabled(true),
-                false);
+                false,
+                1);
     }
 
     public LocalQueryRunner(Session defaultSession, FeaturesConfig featuresConfig)
     {
-        this(defaultSession, featuresConfig, false);
+        this(defaultSession, featuresConfig, false, 1);
     }
 
-    private LocalQueryRunner(Session defaultSession, FeaturesConfig featuresConfig, boolean withInitialTransaction)
+    private LocalQueryRunner(Session defaultSession, FeaturesConfig featuresConfig, boolean withInitialTransaction, int nodeCountForStats)
     {
         requireNonNull(defaultSession, "defaultSession is null");
         checkArgument(!defaultSession.getTransactionId().isPresent() || !withInitialTransaction, "Already in transaction");
@@ -379,14 +380,19 @@ private LocalQueryRunner(Session defaultSession, FeaturesConfig featuresConfig,
                 new CoefficientBasedStatsCalculator(metadata),
                 ServerMainModule.createNewStatsCalculator(metadata, new FilterStatsCalculator(metadata), new ScalarStatsCalculator(metadata)));
         this.costCalculator = new CostCalculatorUsingExchanges(getNodeCount());
-        this.estimatedExchangesCostCalculator = new CostCalculatorWithEstimatedExchanges(costCalculator, getNodeCount());
+        this.estimatedExchangesCostCalculator = new CostCalculatorWithEstimatedExchanges(costCalculator, nodeCountForStats);
         this.lookup = new StatelessLookup(statsCalculator, costCalculator);
     }
 
     public static LocalQueryRunner queryRunnerWithInitialTransaction(Session defaultSession)
     {
         checkArgument(!defaultSession.getTransactionId().isPresent(), "Already in transaction!");
-        return new LocalQueryRunner(defaultSession, new FeaturesConfig(), true);
+        return new LocalQueryRunner(defaultSession, new FeaturesConfig(), true, 1);
+    }
+
+    public static LocalQueryRunner queryRunnerWithFakeNodeCountForStats(Session defaultSession, int nodeCount)
+    {
+        return new LocalQueryRunner(defaultSession, new FeaturesConfig(), false, nodeCount);
     }
 
     @Override