diff --git a/smime_test.go b/smime_test.go
new file mode 100644
index 0000000..bd0282d
--- /dev/null
+++ b/smime_test.go
@@ -0,0 +1,156 @@
+package mail
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"testing"
+)
+
+// TestNewSMime tests the newSMime method
+func TestNewSMime(t *testing.T) {
+	keyPair, err := getDummyCertificate()
+	if err != nil {
+		t.Errorf("Error getting dummy certificate: %s", err)
+	}
+
+	sMime, err := newSMime(keyPair)
+	if err != nil {
+		t.Errorf("Error creating new SMime from keyPair: %s", err)
+	}
+
+	if sMime.privateKey != keyPair.PrivateKey {
+		t.Errorf("NewSMime() did not return the same private key")
+	}
+	if sMime.certificate != keyPair.Leaf {
+		t.Errorf("NewSMime() did not return the same leaf certificate")
+	}
+	if len(sMime.parentCertificates) != len(keyPair.Certificate)-1 {
+		t.Errorf("NewSMime() did not return the same number of parentCertificates")
+	}
+}
+
+// TestSign tests the sign method
+func TestSign(t *testing.T) {
+	keyPair, err := getDummyCertificate()
+	if err != nil {
+		t.Errorf("Error getting dummy certificate: %s", err)
+	}
+
+	sMime, err := newSMime(keyPair)
+	if err != nil {
+		t.Errorf("Error creating new SMime from keyPair: %s", err)
+	}
+	fmt.Println(sMime)
+}
+
+// TestCreateMessage tests the createMessage method
+func TestCreateMessage(t *testing.T) {
+	keyPair, err := getDummyCertificate()
+	if err != nil {
+		t.Errorf("Error getting dummy certificate: %s", err)
+	}
+
+	sMime, err := newSMime(keyPair)
+	if err != nil {
+		t.Errorf("Error creating new SMime from keyPair: %s", err)
+	}
+
+	encoding := EncodingB64
+	contentType := TypeTextPlain
+	charset := CharsetUTF8
+	body := []byte("This is the body!")
+	result := sMime.createMessage(encoding, contentType, body)
+
+	if !strings.Contains(result, encoding.String()) {
+		t.Errorf("createMessage() did not return the correct encoding")
+	}
+	if !strings.Contains(result, contentType.String()) {
+		t.Errorf("createMessage() did not return the correct contentType")
+	}
+	if !strings.Contains(result, string(body)) {
+		t.Errorf("createMessage() did not return the correct body")
+	}
+	if result != fmt.Sprintf("Content-Transfer-Encoding: %v\r\nContent-Type: %v; charset=%v\r\n\r\n%v", encoding, contentType, charset, string(body)) {
+		t.Errorf("createMessage() did not sucessfully create the message")
+	}
+}
+
+// TestEncodeToPEM tests the encodeToPEM method
+func TestEncodeToPEM(t *testing.T) {
+
+	keyPair, err := getDummyCertificate()
+	if err != nil {
+		t.Errorf("Error getting dummy certificate: %s", err)
+	}
+
+	sMime, err := newSMime(keyPair)
+	if err != nil {
+		t.Errorf("Error creating new SMime from keyPair: %s", err)
+	}
+	fmt.Println(sMime)
+}
+
+// TestBytesFromLines tests the bytesFromLines method
+func TestBytesFromLines(t *testing.T) {
+
+}
+
+// TestParseLines tests the parseLines method
+func TestParseLines(t *testing.T) {
+
+}
+
+// TestSplitLine tests the splitLine method
+func TestSplitLine(t *testing.T) {
+
+}
+
+func foo(t *testing.T) {
+	tl := []struct {
+		n  string
+		r  SendErrReason
+		te bool
+	}{
+		{"ErrGetSender/temp", ErrGetSender, true},
+		{"ErrGetSender/perm", ErrGetSender, false},
+		{"ErrGetRcpts/temp", ErrGetRcpts, true},
+		{"ErrGetRcpts/perm", ErrGetRcpts, false},
+		{"ErrSMTPMailFrom/temp", ErrSMTPMailFrom, true},
+		{"ErrSMTPMailFrom/perm", ErrSMTPMailFrom, false},
+		{"ErrSMTPRcptTo/temp", ErrSMTPRcptTo, true},
+		{"ErrSMTPRcptTo/perm", ErrSMTPRcptTo, false},
+		{"ErrSMTPData/temp", ErrSMTPData, true},
+		{"ErrSMTPData/perm", ErrSMTPData, false},
+		{"ErrSMTPDataClose/temp", ErrSMTPDataClose, true},
+		{"ErrSMTPDataClose/perm", ErrSMTPDataClose, false},
+		{"ErrSMTPReset/temp", ErrSMTPReset, true},
+		{"ErrSMTPReset/perm", ErrSMTPReset, false},
+		{"ErrWriteContent/temp", ErrWriteContent, true},
+		{"ErrWriteContent/perm", ErrWriteContent, false},
+		{"ErrConnCheck/temp", ErrConnCheck, true},
+		{"ErrConnCheck/perm", ErrConnCheck, false},
+		{"ErrNoUnencoded/temp", ErrNoUnencoded, true},
+		{"ErrNoUnencoded/perm", ErrNoUnencoded, false},
+		{"ErrAmbiguous/temp", ErrAmbiguous, true},
+		{"ErrAmbiguous/perm", ErrAmbiguous, false},
+		{"Unknown/temp", 9999, true},
+		{"Unknown/perm", 9999, false},
+	}
+
+	for _, tt := range tl {
+		t.Run(tt.n, func(t *testing.T) {
+			if err := returnSendError(tt.r, tt.te); err != nil {
+				exp := &SendError{Reason: tt.r, isTemp: tt.te}
+				if !errors.Is(err, exp) {
+					t.Errorf("error mismatch, expected: %s (temp: %t), got: %s (temp: %t)", tt.r, tt.te,
+						exp.Error(), exp.isTemp)
+				}
+				if !strings.Contains(fmt.Sprintf("%s", err), tt.r.String()) {
+					t.Errorf("error string mismatch, expected: %s, got: %s",
+						tt.r.String(), fmt.Sprintf("%s", err))
+				}
+			}
+		})
+	}
+}