git » chasquid » commit d6bbea3

diff --git a/internal/maillog/maillog_test.go b/internal/maillog/maillog_test.go
index 2a11603..78d32e1 100644
--- a/internal/maillog/maillog_test.go
+++ b/internal/maillog/maillog_test.go
@@ -3,10 +3,13 @@ package maillog
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"net"
 	"strings"
 	"testing"
 	"time"
+
+	"blitiri.com.ar/go/log"
 )
 
 var netAddr = &net.TCPAddr{
@@ -114,3 +117,47 @@ func TestDefault(t *testing.T) {
 	expect(t, buf, "qid from=from all done")
 	buf.Reset()
 }
+
+// io.Writer that fails all write operations, for testing.
+type failedWriter struct{}
+
+func (w *failedWriter) Write(p []byte) (int, error) {
+	return 0, fmt.Errorf("test error")
+}
+
+// nopCloser adds a Close method to an io.Writer, to turn it into a
+// io.WriteCloser. This is the equivalent of ioutil.NopCloser but for
+// io.Writer.
+type nopCloser struct {
+	io.Writer
+}
+
+func (nopCloser) Close() error { return nil }
+
+// Test that we complain (only once) when we can't log.
+func TestFailedLogger(t *testing.T) {
+	// Set up a test logger, that will write to a buffer for us to check.
+	buf := &bytes.Buffer{}
+	log.Default = log.New(nopCloser{io.Writer(buf)})
+
+	// Set up a maillog that will use a writer which always fail, to trigger
+	// the condition.
+	failedw := &failedWriter{}
+	l := New(failedw)
+
+	// Log something, which should fail. Then verify that the error message
+	// appears in the log.
+	l.printf("123 testing")
+	s := buf.String()
+	if !strings.Contains(s, "failed to write to maillog: test error") {
+		t.Errorf("log did not contain expected message. Log: %#v", s)
+	}
+
+	// Further attempts should not generate any other errors.
+	buf.Reset()
+	l.printf("123 testing")
+	s = buf.String()
+	if s != "" {
+		t.Errorf("expected second attempt to not log, but log had: %#v", s)
+	}
+}