diff --git a/dummy-chain-cert.pem b/dummy-chain-cert.pem
new file mode 100644
index 0000000..4daceaa
--- /dev/null
+++ b/dummy-chain-cert.pem
@@ -0,0 +1,62 @@
+-----BEGIN CERTIFICATE-----
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+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
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+-----END CERTIFICATE-----
diff --git a/dummy-child-key.pem b/dummy-child-key.pem
new file mode 100644
index 0000000..2a8639b
--- /dev/null
+++ b/dummy-child-key.pem
@@ -0,0 +1,52 @@
+-----BEGIN PRIVATE KEY-----
+MIIJQAIBADANBgkqhkiG9w0BAQEFAASCCSowggkmAgEAAoICAQCiLh0JJTRRBhmU
+yiMKALHtTOK7T20Bwy+fG0SO6RlBc+hSuuX/n6znXcNgOBlQ2Gg3+p1on/bmcKnG
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+S++xGnGHEUSEl7cWnO8k0RyJzzc=
+-----END PRIVATE KEY-----
diff --git a/msg_test.go b/msg_test.go
index 6e35d49..9464a50 100644
--- a/msg_test.go
+++ b/msg_test.go
@@ -3345,8 +3345,9 @@ func TestMsg_signMessage(t *testing.T) {
 	if err != nil {
 		t.Errorf("failed to load dummy certificate. Cause: %v", err)
 	}
-	m := NewMsg()
 	body := []byte("This is the body")
+	m := NewMsg()
+	m.SetBodyString(TypeTextPlain, string(body))
 	if err := m.SignWithSMime(keyPair); err != nil {
 		t.Errorf("set of certificate was not successful")
 	}
diff --git a/util_test.go b/util_test.go
index 8f235ed..47bac43 100644
--- a/util_test.go
+++ b/util_test.go
@@ -2,11 +2,12 @@ package mail
 
 import (
 	"crypto/tls"
+	"crypto/x509"
 )
 
 const (
-	certFilePath = "dummy-cert.pem"
-	keyFilePath  = "dummy=key.pem"
+	certFilePath = "dummy-chain-cert.pem"
+	keyFilePath  = "dummy-child-key.pem"
 )
 
 func getDummyCertificate() (*tls.Certificate, error) {
@@ -15,5 +16,7 @@ func getDummyCertificate() (*tls.Certificate, error) {
 		return nil, err
 	}
 
+	keyPair.Leaf, err = x509.ParseCertificate(keyPair.Certificate[0])
+
 	return &keyPair, nil
 }