diff --git a/msgwriter_test.go b/msgwriter_test.go
new file mode 100644
index 0000000..856616d
--- /dev/null
+++ b/msgwriter_test.go
@@ -0,0 +1,102 @@
+package mail
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"mime"
+	"strings"
+	"testing"
+	"time"
+)
+
+// brokenWriter implements a broken writer for io.Writer testing
+type brokenWriter struct {
+	io.Writer
+}
+
+// Write implements the io.Writer interface but intentionally returns an error at
+// any time
+func (bw *brokenWriter) Write([]byte) (int, error) {
+	return 0, fmt.Errorf("intentionally failed")
+}
+
+// TestMsgWriter_Write tests the Write() method of the msgWriter
+func TestMsgWriter_Write(t *testing.T) {
+	bw := &brokenWriter{}
+	mw := &msgWriter{w: bw, c: CharsetUTF8, en: mime.QEncoding}
+	_, err := mw.Write([]byte("test"))
+	if err == nil {
+		t.Errorf("msgWriter Write() with brokenWriter should fail, but didn't")
+	}
+
+	// Also test the part when a previous error happend
+	mw.err = fmt.Errorf("broken")
+	_, err = mw.Write([]byte("test"))
+	if err == nil {
+		t.Errorf("msgWriter Write() with brokenWriter should fail, but didn't")
+	}
+}
+
+// TestMsgWriter_writeMsg tests the writeMsg method of the msgWriter
+func TestMsgWriter_writeMsg(t *testing.T) {
+	m := NewMsg()
+	_ = m.From(`"Toni Tester" <test@example.com>`)
+	_ = m.To(`"Toni Receiver" <receiver@example.com>`)
+	m.Subject("This is a subject")
+	m.SetBulk()
+	now := time.Now()
+	m.SetDateWithValue(now)
+	m.SetMessageIDWithValue("message@id.com")
+	m.SetBodyString(TypeTextPlain, "This is the body")
+	buf := bytes.Buffer{}
+	mw := &msgWriter{w: &buf, c: CharsetUTF8, en: mime.QEncoding}
+	mw.writeMsg(m)
+	ms := buf.String()
+
+	var ea []string
+	if !strings.Contains(ms, `MIME-Version: 1.0`) {
+		ea = append(ea, "MIME-Version")
+	}
+	if !strings.Contains(ms, fmt.Sprintf("Date: %s", now.Format(time.RFC1123Z))) {
+		ea = append(ea, "Date")
+	}
+	if !strings.Contains(ms, `Message-ID: <message@id.com>`) {
+		ea = append(ea, "Message-ID")
+	}
+	if !strings.Contains(ms, `Precedence: bulk`) {
+		ea = append(ea, "Precedence")
+	}
+	if !strings.Contains(ms, `Subject: This is a subject`) {
+		ea = append(ea, "Subject")
+	}
+	if !strings.Contains(ms, `User-Agent: go-mail v`) {
+		ea = append(ea, "User-Agent")
+	}
+	if !strings.Contains(ms, `X-Mailer: go-mail v`) {
+		ea = append(ea, "X-Mailer")
+	}
+	if !strings.Contains(ms, `From: "Toni Tester" <test@example.com>`) {
+		ea = append(ea, "From")
+	}
+	if !strings.Contains(ms, `To: "Toni Receiver" <receiver@example.com>`) {
+		ea = append(ea, "To")
+	}
+	if !strings.Contains(ms, `Content-Type: text/plain; charset=UTF-8`) {
+		ea = append(ea, "Content-Type")
+	}
+	if !strings.Contains(ms, `Content-Transfer-Encoding: quoted-printable`) {
+		ea = append(ea, "Content-Transfer-Encoding")
+	}
+	if !strings.Contains(ms, "\r\n\r\nThis is the body") {
+		ea = append(ea, "Message body")
+	}
+	if len(ea) > 0 {
+		em := fmt.Sprint("writeMsg() failed. The following errors occured:\n")
+		for e := range ea {
+			em += fmt.Sprintf("* incorrect %q field", ea[e])
+		}
+		em += fmt.Sprintf("\n\nFull message:\n%s", ms)
+		t.Errorf(em)
+	}
+}