diff --git a/coordinator/src/main/scala/filodb.coordinator/queryplanner/LogicalPlanUtils.scala b/coordinator/src/main/scala/filodb.coordinator/queryplanner/LogicalPlanUtils.scala
index 4900c35b63..6f028fb5d5 100644
--- a/coordinator/src/main/scala/filodb.coordinator/queryplanner/LogicalPlanUtils.scala
+++ b/coordinator/src/main/scala/filodb.coordinator/queryplanner/LogicalPlanUtils.scala
@@ -422,9 +422,9 @@ object LogicalPlanUtils extends StrictLogging {
    *   - all plan RawSeries share the same target-schema columns.
    *   - no target-schema definition changes during the query.
    */
-  private def sameRawSeriesTargetSchemaColumns(plan: LogicalPlan,
-                                               targetSchemaProvider: TargetSchemaProvider,
-                                               getShardKeyFilters: RawSeries => Seq[Seq[ColumnFilter]])
+  def sameRawSeriesTargetSchemaColumns(plan: LogicalPlan,
+                                       targetSchemaProvider: TargetSchemaProvider,
+                                       getShardKeyFilters: RawSeries => Seq[Seq[ColumnFilter]])
   : Option[Seq[String]] = {
     // compose a stream of Options for each RawSeries--
     //   the options contain a target-schema iff it is defined and unchanging.
diff --git a/coordinator/src/test/scala/filodb.coordinator/queryplanner/LogicalPlanUtilsSpec.scala b/coordinator/src/test/scala/filodb.coordinator/queryplanner/LogicalPlanUtilsSpec.scala
new file mode 100644
index 0000000000..fa013144db
--- /dev/null
+++ b/coordinator/src/test/scala/filodb.coordinator/queryplanner/LogicalPlanUtilsSpec.scala
@@ -0,0 +1,61 @@
+package filodb.coordinator.queryplanner
+
+import filodb.coordinator.client.QueryCommands.FunctionalTargetSchemaProvider
+import filodb.core.TargetSchemaChange
+import filodb.core.query.ColumnFilter
+import filodb.core.query.Filter.Equals
+import filodb.prometheus.ast.TimeStepParams
+import filodb.prometheus.parse.Parser
+import filodb.query.LogicalPlan
+import org.scalatest.funspec.AnyFunSpec
+import org.scalatest.matchers.should.Matchers
+
+class LogicalPlanUtilsSpec   extends AnyFunSpec with Matchers {
+  it ("should correctly determine whether-or-not plan has same/unchanging target-schema columns") {
+    val timeParamsSec = TimeStepParams(1000, 10, 10000)
+    val timeParamsMs = TimeStepParams(
+      1000 * timeParamsSec.start,
+      1000 * timeParamsSec.step,
+      1000 * timeParamsSec.end)
+    val query = """foo{operand="lhs"} + bar{operand="rhs"}"""
+
+    val getResult = (tschemaProviderFunc: Seq[ColumnFilter] => Seq[TargetSchemaChange]) => {
+      val tschemaProvider = FunctionalTargetSchemaProvider(tschemaProviderFunc)
+      val lp = Parser.queryRangeToLogicalPlan(query, timeParamsSec)
+      LogicalPlanUtils.sameRawSeriesTargetSchemaColumns(lp, tschemaProvider, LogicalPlan.getRawSeriesFilters)
+    }
+
+    val unchangingSingle = (colFilters: Seq[ColumnFilter]) => {
+      Seq(TargetSchemaChange(0, Seq("hello")))
+    }
+    getResult(unchangingSingle) shouldEqual Some(Seq("hello"))
+
+    val unchangingMultiple = (colFilters: Seq[ColumnFilter]) => {
+      Seq(TargetSchemaChange(0, Seq("hello", "goodbye")))
+    }
+    getResult(unchangingMultiple) shouldEqual Some(Seq("hello", "goodbye"))
+
+    val changingSingle = (colFilters: Seq[ColumnFilter]) => {
+      Seq(TargetSchemaChange(timeParamsMs.start + timeParamsMs.step, Seq("hello")))
+    }
+    getResult(changingSingle) shouldEqual None
+
+    val oneChanges = (colFilters: Seq[ColumnFilter]) => {
+      if (colFilters.contains(ColumnFilter("operand", Equals("lhs")))) {
+        Seq(TargetSchemaChange(0, Seq("hello")))
+      } else {
+        Seq(TargetSchemaChange(timeParamsMs.start + timeParamsMs.step, Seq("hello")))
+      }
+    }
+    getResult(oneChanges) shouldEqual None
+
+    val differentCols = (colFilters: Seq[ColumnFilter]) => {
+      if (colFilters.contains(ColumnFilter("operand", Equals("lhs")))) {
+        Seq(TargetSchemaChange(0, Seq("hello")))
+      } else {
+        Seq(TargetSchemaChange(0, Seq("goodbye")))
+      }
+    }
+    getResult(differentCols) shouldEqual None
+  }
+}