make the buffered qlog writer used in interop flush before closing

internal/utils/buffered_write_closer_test.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"bufio"
+	"bytes"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+type nopCloser struct{}
+
+func (nopCloser) Close() error { return nil }
+
+var _ = Describe("buffered io.WriteCloser", func() {
+	It("flushes before closing", func() {
+		buf := &bytes.Buffer{}
+
+		w := bufio.NewWriter(buf)
+		wc := NewBufferedWriteCloser(w, &nopCloser{})
+		wc.Write([]byte("foobar"))
+		Expect(buf.Len()).To(BeZero())
+		Expect(wc.Close()).To(Succeed())
+		Expect(buf.String()).To(Equal("foobar"))
+	})
+})