Test: Protect auto_date_histo from 0 buckets

The test for `auto_date_histogram` as trying to round `Long.MAX_VALUE`
if there were 0 buckets. That doesn't work.

Also, this replaces all of the class variables created to make
consistent random result when testing `InternalAutoDateHistogram` with
the newer `randomResultsToReduce` which is a little simpler to
understand.

Author: nik9000

server/src/test/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogramTests.java

@@ -53,35 +53,19 @@
 import static org.hamcrest.Matchers.hasSize;
 
 public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregationTestCase<InternalAutoDateHistogram> {
-
-    private DocValueFormat format;
-    private RoundingInfo[] roundingInfos;
-    private long defaultStart;
-    private int roundingIndex;
-
-    @Override
-    public void setUp() throws Exception {
-        super.setUp();
-        format = randomNumericDocValueFormat();
-        defaultStart = randomLongBetween(0, utcMillis("2050-01-01"));
-        roundingIndex = between(0, AutoDateHistogramAggregationBuilder.buildRoundings(null, null).length - 1);
-    }
-
-    @Override
-    protected InternalAutoDateHistogram createTestInstance(String name,
-                                                       Map<String, Object> metadata,
-                                                       InternalAggregations aggregations) {
-
-        roundingInfos = AutoDateHistogramAggregationBuilder.buildRoundings(null, null);
+    protected InternalAutoDateHistogram createTestInstance(
+        String name,
+        Map<String, Object> metadata,
+        InternalAggregations aggregations,
+        long startingDate,
+        RoundingInfo[] roundingInfos,
+        int roundingIndex,
+        DocValueFormat format
+    ) {
         int nbBuckets = randomNumberOfBuckets();
         int targetBuckets = randomIntBetween(1, nbBuckets * 2 + 1);
         List<InternalAutoDateHistogram.Bucket> buckets = new ArrayList<>(nbBuckets);
 
-        long startingDate = defaultStart;
-        if (rarely()) {
-            startingDate += randomFrom(TimeUnit.MINUTES, TimeUnit.HOURS, TimeUnit.DAYS).toMillis(between(1, 10000));
-        }
-
         long interval = randomIntBetween(1, 3);
         long intervalMillis = roundingInfos[roundingIndex].roughEstimateDurationMillis * interval;
 
@@ -94,9 +78,26 @@ protected InternalAutoDateHistogram createTestInstance(String name,
         return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, format, metadata, 1);
     }
 
+    @Override
+    protected InternalAutoDateHistogram createTestInstance(String name,
+                                                       Map<String, Object> metadata,
+                                                       InternalAggregations aggregations) {
+        RoundingInfo[] roundingInfos = AutoDateHistogramAggregationBuilder.buildRoundings(null, null);
+        int roundingIndex = between(0, roundingInfos.length - 1);
+        return createTestInstance(
+            name,
+            metadata,
+            aggregations,
+            randomLongBetween(0, utcMillis("2050-01-01")),
+            roundingInfos,
+            roundingIndex,
+            randomNumericDocValueFormat()
+        );
+    }
+
     /*
-    This test was added to reproduce a bug where getAppropriateRounding was only ever using the first innerIntervals
-    passed in, instead of using the interval associated with the loop.
+     * This test was added to reproduce a bug where getAppropriateRounding was only ever using the first innerIntervals
+     * passed in, instead of using the interval associated with the loop.
      */
     public void testGetAppropriateRoundingUsesCorrectIntervals() {
         RoundingInfo[] roundings = new RoundingInfo[6];
@@ -121,8 +122,23 @@ public void testGetAppropriateRoundingUsesCorrectIntervals() {
     }
 
     @Override
-    protected void assertReduced(InternalAutoDateHistogram reduced, List<InternalAutoDateHistogram> inputs) {
+    protected List<InternalAutoDateHistogram> randomResultsToReduce(String name, int size) {
+        long startingDate = randomLongBetween(0, utcMillis("2050-01-01"));
+        RoundingInfo[] roundingInfos = AutoDateHistogramAggregationBuilder.buildRoundings(null, null);
+        int roundingIndex = between(0, roundingInfos.length - 1);
+        DocValueFormat format = randomNumericDocValueFormat();
+        List<InternalAutoDateHistogram> result = new ArrayList<>(size);
+        for (int i = 0; i < size; i++) {
+            long thisResultStart = startingDate;
+            thisResultStart += usually() ? 0 :randomFrom(TimeUnit.MINUTES, TimeUnit.HOURS, TimeUnit.DAYS).toMillis(between(1, 10000));
+            result.add(createTestInstance(name, null, InternalAggregations.EMPTY, thisResultStart, roundingInfos, roundingIndex, format));
+        }
+        return result;
+    }
 
+    @Override
+    protected void assertReduced(InternalAutoDateHistogram reduced, List<InternalAutoDateHistogram> inputs) {
+        int totalBucketConut = 0;
         long lowest = Long.MAX_VALUE;
         long highest = 0;
 
@@ -135,11 +151,12 @@ protected void assertReduced(InternalAutoDateHistogram reduced, List<InternalAut
                 if (bucketKey > highest) {
                     highest = bucketKey;
                 }
+                totalBucketConut++;
             }
         }
 
         int roundingIndex = reduced.getBucketInfo().roundingIdx;
-        RoundingInfo roundingInfo = roundingInfos[roundingIndex];
+        RoundingInfo roundingInfo = AutoDateHistogramAggregationBuilder.buildRoundings(null, null)[roundingIndex];
 
         long normalizedDuration = (highest - lowest) / roundingInfo.getRoughEstimateDurationMillis();
         int innerIntervalIndex = 0;
@@ -163,53 +180,58 @@ protected void assertReduced(InternalAutoDateHistogram reduced, List<InternalAut
          * number of buckets.
          */
         int innerIntervalToUse;
-        do {
-            innerIntervalToUse = roundingInfo.innerIntervals[innerIntervalIndex];
-            int bucketCount = getBucketCount(lowest, highest, roundingInfo.rounding, innerIntervalToUse);
-            if (bucketCount == reduced.getBuckets().size()) {
-                break;
-            }
-            if (bucketCount < reduced.getBuckets().size()) {
-                innerIntervalToUse = roundingInfo.innerIntervals[Math.max(0, innerIntervalIndex - 1)];
-                break;
-            }
-        } while (++innerIntervalIndex < roundingInfo.innerIntervals.length);
+        if (totalBucketConut == 0) {
+            innerIntervalToUse = roundingInfo.innerIntervals[0];
+        } else {
+            do {
+                innerIntervalToUse = roundingInfo.innerIntervals[innerIntervalIndex];
+                int bucketCountAtInterval = getBucketCount(lowest, highest, roundingInfo.rounding, innerIntervalToUse);
+                if (bucketCountAtInterval == reduced.getBuckets().size()) {
+                    break;
+                }
+                if (bucketCountAtInterval < reduced.getBuckets().size()) {
+                    innerIntervalToUse = roundingInfo.innerIntervals[Math.max(0, innerIntervalIndex - 1)];
+                    break;
+                }
+            } while (++innerIntervalIndex < roundingInfo.innerIntervals.length);
+        }
 
         assertThat(reduced.getInterval().toString(), equalTo(innerIntervalToUse + roundingInfo.unitAbbreviation));
         Map<Instant, Long> expectedCounts = new TreeMap<>();
-        long keyForBucket = roundingInfo.rounding.round(lowest);
-        while (keyForBucket <= roundingInfo.rounding.round(highest)) {
-            long nextKey = keyForBucket;
-            for (int i = 0; i < innerIntervalToUse; i++) {
-                nextKey = roundingInfo.rounding.nextRoundingValue(nextKey);
-            }
-            Instant key = Instant.ofEpochMilli(keyForBucket);
-            expectedCounts.put(key, 0L);
-
-            // Iterate through the input buckets, and for each bucket, determine if it's inside
-            // the range of the bucket in the outer loop. if it is, add the doc count to the total
-            // for that bucket.
-
-            for (InternalAutoDateHistogram histogram : inputs) {
-                for (Histogram.Bucket bucket : histogram.getBuckets()) {
-                    long roundedBucketKey = roundingInfo.rounding.round(((ZonedDateTime) bucket.getKey()).toInstant().toEpochMilli());
-                    long docCount = bucket.getDocCount();
-                    if (roundedBucketKey >= keyForBucket && roundedBucketKey < nextKey) {
-                        expectedCounts.compute(key,
-                            (k, oldValue) -> (oldValue == null ? 0 : oldValue) + docCount);
+        if (totalBucketConut > 0) {
+            long keyForBucket = roundingInfo.rounding.round(lowest);
+            while (keyForBucket <= roundingInfo.rounding.round(highest)) {
+                long nextKey = keyForBucket;
+                for (int i = 0; i < innerIntervalToUse; i++) {
+                    nextKey = roundingInfo.rounding.nextRoundingValue(nextKey);
+                }
+                Instant key = Instant.ofEpochMilli(keyForBucket);
+                expectedCounts.put(key, 0L);
+
+                // Iterate through the input buckets, and for each bucket, determine if it's inside
+                // the range of the bucket in the outer loop. if it is, add the doc count to the total
+                // for that bucket.
+
+                for (InternalAutoDateHistogram histogram : inputs) {
+                    for (Histogram.Bucket bucket : histogram.getBuckets()) {
+                        long roundedBucketKey = roundingInfo.rounding.round(((ZonedDateTime) bucket.getKey()).toInstant().toEpochMilli());
+                        long docCount = bucket.getDocCount();
+                        if (roundedBucketKey >= keyForBucket && roundedBucketKey < nextKey) {
+                            expectedCounts.compute(key,
+                                (k, oldValue) -> (oldValue == null ? 0 : oldValue) + docCount);
+                        }
                     }
                 }
+                keyForBucket = nextKey;
             }
-            keyForBucket = nextKey;
-        }
 
-        // If there is only a single bucket, and we haven't added it above, add a bucket with no documents.
-        // this step is necessary because of the roundedBucketKey < keyForBucket + intervalInMillis above.
-        if (roundingInfo.rounding.round(lowest) == roundingInfo.rounding.round(highest) && expectedCounts.isEmpty()) {
-            expectedCounts.put(Instant.ofEpochMilli(roundingInfo.rounding.round(lowest)), 0L);
+            // If there is only a single bucket, and we haven't added it above, add a bucket with no documents.
+            // this step is necessary because of the roundedBucketKey < keyForBucket + intervalInMillis above.
+            if (roundingInfo.rounding.round(lowest) == roundingInfo.rounding.round(highest) && expectedCounts.isEmpty()) {
+                expectedCounts.put(Instant.ofEpochMilli(roundingInfo.rounding.round(lowest)), 0L);
+            }
         }
 
-
         // pick out the actual reduced values to the make the assertion more readable
         Map<Instant, Long> actualCounts = new TreeMap<>();
         for (Histogram.Bucket bucket : reduced.getBuckets()) {
@@ -257,7 +279,7 @@ protected InternalAutoDateHistogram mutateInstance(InternalAutoDateHistogram ins
             break;
         case 1:
             buckets = new ArrayList<>(buckets);
-            buckets.add(new InternalAutoDateHistogram.Bucket(randomNonNegativeLong(), randomIntBetween(1, 100), format,
+            buckets.add(new InternalAutoDateHistogram.Bucket(randomNonNegativeLong(), randomIntBetween(1, 100), instance.getFormatter(),
                     InternalAggregations.EMPTY));
             break;
         case 2:
@@ -275,7 +297,7 @@ protected InternalAutoDateHistogram mutateInstance(InternalAutoDateHistogram ins
         default:
             throw new AssertionError("Illegal randomisation branch");
         }
-        return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, format, metadata, 1);
+        return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, instance.getFormatter(), metadata, 1);
     }
 
     public void testReduceSecond() {