package main_test

import (
	"runtime"
	"testing"
)

var (
	setGCPercentBallast interface{}
	setGCPercentSink    interface{}
)

func TestGC(t *testing.T) {
	defer func() {
		setGCPercentBallast = nil
		setGCPercentSink = nil
		runtime.GC()
	}()

	runtime.GC()
	var m1 runtime.MemStats
	runtime.ReadMemStats(&m1)

	// Create 50 MB of live heap as a baseline.
	const baseline = 50 << 20
	setGCPercentBallast = make([]byte, baseline-m1.Alloc)
	// Disable GOGC-based policy.
	// Set max heap to 2x baseline.
	const limit = 2 * baseline

	// Allocate a bunch and check that we stay under the limit.
	runtime.ReadMemStats(&m1)
	var m2 runtime.MemStats
	for i := 0; i < 200; i++ {
		setGCPercentSink = make([]byte, 1<<20)
		runtime.ReadMemStats(&m2)
		if m2.HeapAlloc > limit {
			t.Logf("HeapAlloc %d exceeds heap limit %d\n", m2.HeapAlloc, limit)
		}
	}
	if m1.NumGC == m2.NumGC {
		t.Fatalf("failed to trigger GC")
	}
}