Merge pull request #205: PackfileMaintenanceStepTests: fix flaky tests

The PackfileMaintenanceStepTests have been failing periodically, and
mostly with failures in RepackAllToOnePack() leading to a failure in
ExpireAllButOneAndKeep().

The way we "force" Git to repack all is to provide a custom batch size.
This batch size used to mean "repack all pack-files with size at most
X until reaching a size of at least X". By specifying "total size - 1",
this required repacking all objects.

HOWEVER, the new logic actually computes an "expected" size of the
objects in a pack that are referenced by the multi-pack-index. If we
have duplicate objects, then those objects can cause two types of error:

1. The duplicates reduce the total expected size below the batch size.

2. The computation of "total expected size" causes round-off error.

Both types of error under-count the number of bytes in the final
pack-file.

By changing the batch size to "total size - min size + 1" we ensure the
following:

  I. The batch size is larger than the maximum pack size.

 II. Every pack-file is required to reach the batch size.

III. We have minimized the chance that duplicate objects will drop
     below this threshold.

With the use of gvfs-helper, we have less control over the pack-files
that are downloaded as part of the clone operation. At minimum, with
this change we should be in a better state than before.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Scalar.FunctionalTests/Tests/EnlistmentPerFixture/PackfileMaintenanceStepTests.cs

@@ -2,6 +2,7 @@
 using Scalar.FunctionalTests.FileSystemRunners;
 using Scalar.FunctionalTests.Tools;
 using Scalar.Tests.Should;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -27,7 +28,11 @@ public PackfileMaintenanceStepTests()
         [TestCase, Order(1)]
         public void RepackAllToOnePack()
         {
-            this.GetPackSizes(out int beforeFetchCommitsAndTreesPackCount, out long maxSize, out long totalSize);
+            this.GetPackSizes(
+                    out int beforeFetchCommitsAndTreesPackCount,
+                    out long maxSize,
+                    out long minSize,
+                    out long totalSize);
 
             // Cannot be sure of the count, but there should be two from the inital clone
             beforeFetchCommitsAndTreesPackCount.ShouldBeAtLeast(2);
@@ -41,13 +46,13 @@ public void RepackAllToOnePack()
             // Run the step to ensure we don't have any packs that will be expired during the repack step
             this.Enlistment.PackfileMaintenanceStep();
 
-            this.GetPackSizes(out int afterPrefetchPackCount, out maxSize, out totalSize);
+            this.GetPackSizes(out int afterPrefetchPackCount, out maxSize, out minSize, out totalSize);
 
             // Cannot be sure of the count, as the fetch-commits-and-trees uses parallel threads to get multiple packs
             afterPrefetchPackCount.ShouldBeAtLeast(2);
 
-            this.Enlistment.PackfileMaintenanceStep(batchSize: totalSize - 1);
-            this.GetPackSizes(out int packCount, out maxSize, out totalSize);
+            this.Enlistment.PackfileMaintenanceStep(batchSize: totalSize - minSize + 1);
+            this.GetPackSizes(out int packCount, out maxSize, out minSize, out totalSize);
 
             // We should not have expired any packs, but created a new one with repack
             packCount.ShouldEqual(afterPrefetchPackCount + 1, $"incorrect number of packs after repack step: {packCount}");
@@ -76,10 +81,11 @@ private List<string> GetPackfiles()
             return Directory.GetFiles(this.PackRoot, "*.pack").ToList();
         }
 
-        private void GetPackSizes(out int packCount, out long maxSize, out long totalSize)
+        private void GetPackSizes(out int packCount, out long maxSize, out long minSize, out long totalSize)
         {
             totalSize = 0;
             maxSize = 0;
+            minSize = long.MaxValue;
             packCount = 0;
 
             foreach (string file in this.GetPackfiles())
@@ -92,6 +98,11 @@ private void GetPackSizes(out int packCount, out long maxSize, out long totalSiz
                 {
                     maxSize = size;
                 }
+
+                if (size < minSize)
+                {
+                    minSize = size;
+                }
             }
         }
     }