query: add regression test for frontier trimming

Author: Schwarf

query/shortest_test.go

@@ -0,0 +1,33 @@
+package query
+
+import (
+	"container/heap"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPriorityQueueTrimToMax_RemovesHighestCost(t *testing.T) {
+	var pq priorityQueue
+	heap.Init(&pq)
+
+	costs := []float64{1, 50, 2, 60, 3, 70, 4}
+	for _, c := range costs {
+		heap.Push(&pq, &queueItem{cost: c})
+	}
+
+	// Trim to keep N-1 elements.
+	(&pq).TrimToMax(int64(len(costs) - 1))
+	require.Equal(t, len(costs)-1, pq.Len())
+
+	// Pop all remaining costs and ensure the maximum was removed.
+	seen := make(map[float64]bool, len(costs))
+	for pq.Len() > 0 {
+		seen[heap.Pop(&pq).(*queueItem).cost] = true
+	}
+
+	require.False(t, seen[70], "expected highest cost to be removed")
+	for _, c := range []float64{1, 2, 3, 4, 50, 60} {
+		require.True(t, seen[c], "expected cost to remain: %v", c)
+	}
+}