GODT-1159 SMTP server not restarting after restored internet

- [x] write tests to check that IMAP and SMTP servers are closed when there
  is no internet
- [x] always create new go-smtp instance during listenAndServe(int)

test/mocks/imap_client.go

@@ -43,6 +43,9 @@ type IMAPClient struct {
 func NewIMAPClient(t TestingT, tag string, imapAddr string) *IMAPClient {
 	conn, err := net.Dial("tcp", imapAddr)
 	require.NoError(t, err)
+	if err != nil {
+		return &IMAPClient{}
+	}
 	response := bufio.NewReader(conn)
 
 	// Read first response to opening connection.

test/mocks/imap_response.go

@@ -117,7 +117,7 @@ func (ir *IMAPResponse) AssertResult(wantResult string) *IMAPResponse {
 func (ir *IMAPResponse) AssertError(wantErrMsg string) *IMAPResponse {
 	ir.wait()
 	if ir.err == nil {
-		a.Fail(ir.t, "Expected error %s", wantErrMsg)
+		a.Fail(ir.t, "Error is nil", "Expected to have %q", wantErrMsg)
 	} else {
 		a.Regexp(ir.t, wantErrMsg, ir.err.Error(), "Expected error %s but got %s", wantErrMsg, ir.err)
 	}

test/mocks/smtp.go

@@ -30,6 +30,7 @@ import (
 
 	"github.com/ProtonMail/go-rfc5322"
 	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -46,6 +47,12 @@ type SMTPClient struct {
 func NewSMTPClient(t TestingT, tag, smtpAddr string) *SMTPClient {
 	conn, err := net.Dial("tcp", smtpAddr)
 	require.NoError(t, err)
+	if err != nil {
+		return &SMTPClient{}
+	}
+	logrus.WithField("addr", conn.LocalAddr().String()).
+		WithField("tag", tag).
+		Debug("SMTP Dialed")
 	response := bufio.NewReader(conn)
 
 	// Read first response to opening connection.
@@ -85,6 +92,7 @@ func (c *SMTPClient) SendCommands(commands ...string) *SMTPResponse {
 		message, err := c.response.ReadString('\n')
 		if err != nil {
 			smtpResponse.err = fmt.Errorf("read response failed: %v", err)
+			c.debug.printErr(smtpResponse.err.Error() + "\n")
 			return smtpResponse
 		}
 

test/mocks/smtp_response.go

@@ -34,7 +34,7 @@ func (sr *SMTPResponse) AssertOK() *SMTPResponse {
 
 func (sr *SMTPResponse) AssertError(wantErrMsg string) *SMTPResponse {
 	if sr.err == nil {
-		a.Fail(sr.t, "Expected error %s", wantErrMsg)
+		a.Fail(sr.t, "Error is nil", "Expected to have %q", wantErrMsg)
 	} else {
 		a.Regexp(sr.t, wantErrMsg, sr.err.Error(), "Expected error %s but got %s", wantErrMsg, sr.err)
 	}