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Fix TestShuffleDERPMapDeterministic flakiness by ensuring deterministic region iteration

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The test was flaky because Go's map iteration order is non-deterministic. Even with a fixed random seed, shuffling regions in different orders produces different results since each shuffle advances the RNG state.

Solution: Sort region IDs before iterating to ensure consistent shuffle order across all test runs.

Co-authored-by: kradalby <98431+kradalby@users.noreply.github.com>
This commit is contained in:
copilot-swe-agent[bot]
2025-11-01 07:13:55 +00:00
parent 6bb7f4383e
commit 1980ee6ca4
2 changed files with 16 additions and 5 deletions
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13
hscontrol/derp/derp.go
View File

@@ -12,6 +12,7 @@ import (
"net/url"
"os"
"reflect"
"slices"
"sync"
"time"
@@ -126,7 +127,17 @@ func shuffleDERPMap(dm *tailcfg.DERPMap) {
return
}
for id, region := range dm.Regions {
// Collect region IDs and sort them to ensure deterministic iteration order.
// Map iteration order is non-deterministic in Go, which would cause the
// shuffle to be non-deterministic even with a fixed seed.
ids := make([]int, 0, len(dm.Regions))
for id := range dm.Regions {
ids = append(ids, id)
}
slices.Sort(ids)
for _, id := range ids {
region := dm.Regions[id]
if len(region.Nodes) == 0 {
continue
}

8
hscontrol/derp/derp_test.go
View File

@@ -83,9 +83,9 @@ func TestShuffleDERPMapDeterministic(t *testing.T) {
RegionCode: "sea",
RegionName: "Seattle",
Nodes: []*tailcfg.DERPNode{
{Name: "10b", RegionID: 10, HostName: "derp10b.tailscale.com"},
{Name: "10c", RegionID: 10, HostName: "derp10c.tailscale.com"},
{Name: "10d", RegionID: 10, HostName: "derp10d.tailscale.com"},
{Name: "10c", RegionID: 10, HostName: "derp10c.tailscale.com"},
{Name: "10b", RegionID: 10, HostName: "derp10b.tailscale.com"},
},
},
2: {
@@ -93,9 +93,9 @@ func TestShuffleDERPMapDeterministic(t *testing.T) {
RegionCode: "sfo",
RegionName: "San Francisco",
Nodes: []*tailcfg.DERPNode{
{Name: "2f", RegionID: 2, HostName: "derp2f.tailscale.com"},
{Name: "2e", RegionID: 2, HostName: "derp2e.tailscale.com"},
{Name: "2d", RegionID: 2, HostName: "derp2d.tailscale.com"},
{Name: "2e", RegionID: 2, HostName: "derp2e.tailscale.com"},
{Name: "2f", RegionID: 2, HostName: "derp2f.tailscale.com"},
},
},
},