From a9a3590bdbb420a5a92c662cc5a9956750098181 Mon Sep 17 00:00:00 2001
From: Anton Klaren <anton.klaren@neotechnology.com>
Date: Tue, 13 Mar 2018 16:38:38 +0100
Subject: [PATCH] Make sure we always read at least one line of data from the
 metric file and try to unflake RotatableCsvOutputIT

---
 .../org/neo4j/metrics/MetricsTestHelper.java  | 11 +++++-
 .../metrics/output/RotatableCsvOutputIT.java  | 35 +++++++++++--------
 2 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/enterprise/metrics/src/test/java/org/neo4j/metrics/MetricsTestHelper.java b/enterprise/metrics/src/test/java/org/neo4j/metrics/MetricsTestHelper.java
index 22542ae198262..cff36508975d6 100644
--- a/enterprise/metrics/src/test/java/org/neo4j/metrics/MetricsTestHelper.java
+++ b/enterprise/metrics/src/test/java/org/neo4j/metrics/MetricsTestHelper.java
@@ -135,7 +135,15 @@ private static <T, FIELD extends Enum<FIELD> & CsvField> T readValueAndAssert( F
 
             T currentValue = startValue;
             String line;
-            while ( (line = reader.readLine()) != null )
+
+            // Always read at least one line of data
+            do
+            {
+                line = reader.readLine();
+            }
+            while ( line == null );
+
+            do
             {
                 String[] fields = line.split( "," );
                 T newValue = parser.apply( fields[metricsValue.ordinal()] );
@@ -143,6 +151,7 @@ private static <T, FIELD extends Enum<FIELD> & CsvField> T readValueAndAssert( F
                         assumption.test( newValue, currentValue ) );
                 currentValue = newValue;
             }
+            while ( (line = reader.readLine()) != null );
             return currentValue;
         }
     }
diff --git a/enterprise/metrics/src/test/java/org/neo4j/metrics/output/RotatableCsvOutputIT.java b/enterprise/metrics/src/test/java/org/neo4j/metrics/output/RotatableCsvOutputIT.java
index 39a799c1ae651..62db57e789eaf 100644
--- a/enterprise/metrics/src/test/java/org/neo4j/metrics/output/RotatableCsvOutputIT.java
+++ b/enterprise/metrics/src/test/java/org/neo4j/metrics/output/RotatableCsvOutputIT.java
@@ -26,6 +26,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.util.function.BiPredicate;
 
 import org.neo4j.graphdb.GraphDatabaseService;
 import org.neo4j.graphdb.Transaction;
@@ -50,6 +51,7 @@ public class RotatableCsvOutputIT
 
     private File outputPath;
     private GraphDatabaseService database;
+    private static final BiPredicate<Long,Long> MONOTONIC = ( newValue, currentValue ) -> newValue >= currentValue;
 
     @Before
     public void setup()
@@ -71,27 +73,32 @@ public void tearDown()
     @Test
     public void rotateMetricsFile() throws InterruptedException, IOException
     {
-        try ( Transaction transaction = database.beginTx() )
-        {
-            database.createNode();
-            transaction.success();
-        }
-        File metricsFile = metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED );
-        long committedTransactions = readLongValueAndAssert( metricsFile,
-                ( newValue, currentValue ) -> newValue >= currentValue );
+        doTransaction();
+
+        // wait for rotation to happen
+        File metricsFile1 = metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED, 1 );
+        long committedTransactions = readLongValueAndAssert( metricsFile1, MONOTONIC );
         assertEquals( 1, committedTransactions );
 
-        metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED, 1 );
+        doTransaction();
+
+        // Wait for rotation, since we rotated twice, file 3 is actually the original file
+        File metricsFile2 = metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED, 2 );
+        long oldCommittedTransactions = readLongValueAndAssert( metricsFile2, MONOTONIC );
+        assertEquals( 1, oldCommittedTransactions );
+
+        File metricsFile = metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED );
+        long lastCommittedTransactions = readLongValueAndAssert( metricsFile, MONOTONIC );
+        assertEquals( 2, lastCommittedTransactions );
+    }
+
+    private void doTransaction()
+    {
         try ( Transaction transaction = database.beginTx() )
         {
             database.createNode();
             transaction.success();
         }
-        // Since we rotated twice, file 3 is actually the original file
-        File metricsFile3 = metricsCsv( outputPath, TransactionMetrics.TX_COMMITTED, 2 );
-        long oldCommittedTransactions = readLongValueAndAssert( metricsFile3,
-                ( newValue, currentValue ) -> newValue >= currentValue );
-        assertEquals( 1, oldCommittedTransactions );
     }
 
     private static File metricsCsv( File dbDir, String metric ) throws InterruptedException