test(agentcompat): harden deterministic fixtures

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/fixture/payload_heap_test.go

@@ -0,0 +1,65 @@
+package fixture
+
+import (
+	"bytes"
+	"io"
+	"runtime"
+	"testing"
+
+	"github.com/nezhahq/nezha/integration/agentcompat/internal/contract"
+)
+
+type retainedHeapReader struct {
+	reader   io.Reader
+	baseline uint64
+	peak     uint64
+}
+
+func verifyPayloadPeakRetainedHeap(reader io.Reader, expectedBytes uint64) (PayloadDigest, uint64, error) {
+	runtime.GC()
+	var baseline runtime.MemStats
+	runtime.ReadMemStats(&baseline)
+	measuredReader := &retainedHeapReader{reader: reader, baseline: baseline.HeapAlloc}
+	digest, err := VerifyPayload(measuredReader, expectedBytes)
+	return digest, measuredReader.peak, err
+}
+
+func (reader *retainedHeapReader) Read(destination []byte) (int, error) {
+	readBytes, err := reader.reader.Read(destination)
+	// Sampling after a forced collection measures the live heap retained by each
+	// streaming checkpoint instead of scheduler-dependent allocation churn.
+	runtime.GC()
+	var sample runtime.MemStats
+	runtime.ReadMemStats(&sample)
+	runtime.KeepAlive(destination)
+	if sample.HeapAlloc > reader.baseline {
+		reader.peak = max(reader.peak, sample.HeapAlloc-reader.baseline)
+	}
+	return readBytes, err
+}
+
+func TestFixture_PeakRetainedHeapDetectsRetainedAllocation(t *testing.T) {
+	// Given
+	reader := &allocationRetainingReader{reader: bytes.NewReader([]byte("x"))}
+
+	// When
+	_, peakRetainedHeap, err := verifyPayloadPeakRetainedHeap(reader, 1)
+	requireNoFixtureError(t, err)
+
+	// Then
+	if peakRetainedHeap <= contract.TransferHeapBytes {
+		t.Fatalf("peak retained heap = %d, want greater than %d", peakRetainedHeap, contract.TransferHeapBytes)
+	}
+}
+
+type allocationRetainingReader struct {
+	reader   io.Reader
+	retained []byte
+}
+
+func (reader *allocationRetainingReader) Read(destination []byte) (int, error) {
+	if reader.retained == nil {
+		reader.retained = make([]byte, contract.TransferHeapBytes+1024*1024)
+	}
+	return reader.reader.Read(destination)
+}