mining: Add tests for prio queue. (#666)

This adds a test to ensure the priority queue works properly both for
sorting by fee per KB and priorities.

Thanks to @ceejep for the original test code and idea which was
subsequently modified and cleaned up a bit to the code here.

mining_test.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2016 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"container/heap"
+	"math/rand"
+	"testing"
+
+	"github.com/btcsuite/btcutil"
+)
+
+// TestTxFeePrioHeap ensures the priority queue for transaction fees and
+// priorities works as expected.
+func TestTxFeePrioHeap(t *testing.T) {
+	// Create priority items with random fees and priorites.
+	const numItems = 1000
+	prioItems := make([]*txPrioItem, numItems)
+	highestFeePerKB := int64(0)
+	highestPrio := float64(0)
+	for i := 0; i < 1000; i++ {
+		randPrio := rand.Float64() * 100
+		if randPrio > highestPrio {
+			highestPrio = randPrio
+		}
+		randFeePerKB := int64(rand.Float64() * btcutil.SatoshiPerBitcoin)
+		if randFeePerKB > highestFeePerKB {
+			highestFeePerKB = randFeePerKB
+		}
+		prioItems[i] = &txPrioItem{
+			tx:       nil,
+			priority: randPrio,
+			feePerKB: randFeePerKB,
+		}
+	}
+
+	// Test sorting by fee per KB.
+	priorityQueue := newTxPriorityQueue(numItems, true)
+	for i := 0; i < numItems; i++ {
+		heap.Push(priorityQueue, prioItems[i])
+	}
+	for i := 0; i < numItems; i++ {
+		prioItem := heap.Pop(priorityQueue).(*txPrioItem)
+		if prioItem.feePerKB > highestFeePerKB {
+			t.Fatalf("bad pop: %v fee per KB was more than last of %v",
+				prioItem.feePerKB, highestFeePerKB)
+		}
+		highestFeePerKB = prioItem.feePerKB
+	}
+
+	// Test sorting by priority.
+	priorityQueue = newTxPriorityQueue(numItems, false)
+	for i := 0; i < numItems; i++ {
+		heap.Push(priorityQueue, prioItems[i])
+	}
+	for i := 0; i < numItems; i++ {
+		prioItem := heap.Pop(priorityQueue).(*txPrioItem)
+		if prioItem.priority > highestPrio {
+			t.Fatalf("bad pop: %v priority was more than last of %v",
+				prioItem.priority, highestPrio)
+		}
+	}
+}