bindings/go: Add memory usage test for streaming parser (#181)

Author: varungandhi-src

bindings/go/scip/memtest/DO_NOT_ADD_NEW_TEST_FILES_HERE

@@ -0,0 +1,4 @@
+This package should only have a single test
+so that we can use SetMemoryLimit without
+affecting other tests running in different
+goroutines in the same process.

bindings/go/scip/memtest/low_mem_test.go

@@ -0,0 +1,63 @@
+package memtest
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"runtime"
+	"runtime/debug"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/proto"
+
+	"github.com/sourcegraph/scip/bindings/go/scip"
+)
+
+// Do not add any other tests in this sub-package, so that the
+// SetMemoryLimit call doesn't interfere with other running tests
+
+func TestLowMemoryParsing(t *testing.T) {
+	tmpFile, err := os.CreateTemp(t.TempDir(), "very-large-index.scip")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpFile.Name())
+
+	// Total index size will be about (textSize + ε) * docCount ~= 128 MB
+	const textSize = 128 * 1024
+	const docCount = 1000
+	{
+		largeIndex := scip.Index{}
+		for i := 0; i < docCount; i++ {
+			doc := scip.Document{}
+			doc.Text = strings.Repeat(fmt.Sprintf("%d", i), textSize)
+			largeIndex.Documents = append(largeIndex.Documents, &doc)
+		}
+		indexBytes, err := proto.Marshal(&largeIndex)
+		require.NoError(t, err)
+		_, err = tmpFile.Write(indexBytes)
+		require.NoError(t, err)
+
+		_, err = tmpFile.Seek(0, io.SeekStart)
+		require.NoError(t, err)
+
+		runtime.GC()
+	}
+
+	require.Greater(t, docCount, 100)
+	const maxDocsInMemory = docCount / 100
+	debug.SetMemoryLimit(textSize * maxDocsInMemory)
+
+	curDoc := &scip.Document{}
+	indexVisitor := scip.IndexVisitor{VisitDocument: func(d *scip.Document) {
+		curDoc = d
+	}}
+
+	// No OOM
+	err = indexVisitor.ParseStreaming(tmpFile)
+	_ = curDoc
+	require.NoError(t, err)
+}
+
+// Do not add any other tests in this sub-package, so that the
+// SetMemoryLimit call doesn't interfere with other running tests