state: add TestReplicaPlacement

This makes it easy to explore the behavior of replica placements.

Author: tbg

pkg/kv/kvserver/asim/state/BUILD.bazel

@@ -55,9 +55,11 @@ go_test(
         "change_test.go",
         "config_loader_test.go",
         "liveness_test.go",
+        "parser_replica_placement_test.go",
         "split_decider_test.go",
         "state_test.go",
     ],
+    data = glob(["testdata/**"]),
     embed = [":state"],
     deps = [
         "//pkg/kv/kvpb",
@@ -66,7 +68,9 @@ go_test(
         "//pkg/kv/kvserver/liveness/livenesspb",
         "//pkg/kv/kvserver/load",
         "//pkg/roachpb",
+        "//pkg/testutils/datapathutils",
         "//pkg/util/hlc",
+        "@com_github_cockroachdb_datadriven//:datadriven",
         "@com_github_stretchr_testify//require",
     ],
 )

pkg/kv/kvserver/asim/state/parser_replica_placement.go

@@ -16,9 +16,11 @@ import (
 
 // ReplicaPlacement is a list of replica placement ratios. Each ratio represents
 // a % of ranges that should be placed using the given store IDs and types. For
-// example, a ratio of {s1:*,s2,s3:NON_VOTER}:1 means 1/3 of ranges should be
-// placed with replicas on s1, s2, and s3, s1 as the leaseholder, and the replica
-// on s3 as a non-voter.
+// example, a ratio of {s1:*,s2,s3:NON_VOTER}:1 present in a ReplicaPlacement of
+// total weight 3 means 1/3 of ranges should be placed with replicas on s1, s2,
+// and s3, s1 as the leaseholder, and the replica on s3 as a non-voter.
+//
+// See TestReplicaPlacement for more examples.
 type ReplicaPlacement []Ratio
 
 // findReplicaPlacementForEveryStoreSet finds the replica placement for every

pkg/kv/kvserver/asim/state/parser_replica_placement_test.go

@@ -0,0 +1,26 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package state
+
+import (
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/testutils/datapathutils"
+	"github.com/cockroachdb/datadriven"
+	"github.com/stretchr/testify/require"
+)
+
+// TestReplicaPlacement tests the ReplicaPlacement parser.
+func TestReplicaPlacement(t *testing.T) {
+	datadriven.Walk(t, datapathutils.TestDataPath(t, t.Name()), func(t *testing.T, path string) {
+		datadriven.RunTest(t, path, func(t *testing.T, d *datadriven.TestData) string {
+			require.Equal(t, "parse", d.Cmd)
+			rp := ParseStoreWeights(d.Input)
+			rp.findReplicaPlacementForEveryStoreSet(1000)
+			return rp.String()
+		})
+	})
+}

pkg/kv/kvserver/asim/state/testdata/TestReplicaPlacement/basic.txt

@@ -0,0 +1,39 @@
+# This test tests ReplicaPlacement parser which is used for
+# placement_type=replica_placement option for gen_ranges command.
+parse
+{s3}:1
+----
+{s3:leaseholder}:1000
+
+parse
+{s3}:7
+----
+{s3:leaseholder}:1000
+
+parse
+{s2:*}:100
+----
+{s2:leaseholder}:1000
+
+parse
+{s2:NON_VOTER,s4:*}:100
+----
+{s2:NON_VOTER,s4:leaseholder}:1000
+
+parse
+{s2:NON_VOTER,s4:*, s1}:100
+----
+{s2:NON_VOTER,s4:leaseholder,s1}:1000
+
+parse
+{s1:*,s2,s3:NON_VOTER}:1 {s4:*,s5,s6}:1
+----
+{s1:leaseholder,s2,s3:NON_VOTER}:500
+{s4:leaseholder,s5,s6}:500
+
+parse
+{s1:NON_VOTER,s2,s3}:10 {s4,s5:*,s6}:10 {s7,s2}:1
+----
+{s1:NON_VOTER:leaseholder,s2,s3}:477
+{s4,s5:leaseholder,s6}:476
+{s7:leaseholder,s2}:47