diff --git a/pytrustnfe/servicos/assinatura.py b/pytrustnfe/servicos/assinatura.py
index 9200fb6..f7f16d3 100644
--- a/pytrustnfe/servicos/assinatura.py
+++ b/pytrustnfe/servicos/assinatura.py
@@ -1,9 +1,11 @@
+#coding=utf-8
 '''
 Created on Jun 14, 2015
 
 @author: danimar
 '''
 import xmlsec, libxml2
+import os.path
 
 NAMESPACE_SIG = 'http://www.w3.org/2000/09/xmldsig#'
 
@@ -12,7 +14,11 @@ class Assinatura(object):
     def __init__(self, arquivo, senha):
         self.arquivo = arquivo
         self.senha = senha
-        
+    
+    def _checar_certificado(self): 
+        if not os.path.isfile(self.arquivo):
+            raise Exception('Caminho do certificado não existe.')
+    
     def _inicializar_cripto(self):
         libxml2.initParser()
         libxml2.substituteEntitiesDefault(1)
@@ -30,6 +36,7 @@ class Assinatura(object):
         
     
     def assina_xml(self, xml):
+        self._checar_certificado()
         self._inicializar_cripto()
         try:
             doc_xml = libxml2.parseMemory(xml.encode('utf-8'), len(xml.encode('utf-8')))
diff --git a/pytrustnfe/test/test_assinatura.py b/pytrustnfe/test/test_assinatura.py
index e261e49..d9aa829 100644
--- a/pytrustnfe/test/test_assinatura.py
+++ b/pytrustnfe/test/test_assinatura.py
@@ -5,27 +5,41 @@ Created on Jun 14, 2015
 @author: danimar
 '''
 import unittest
+import os, os.path
 from pytrustnfe.servicos.assinatura import Assinatura
 
 XML_ASSINAR = '<?xml version="1.0" encoding="UTF-8"?>' \
+               '<!DOCTYPE Envelope [ ' \
+               '     <!ATTLIST Data Id ID #IMPLIED>' \
+               ']>' \
                '<Envelope xmlns="urn:envelope">'  \
                '   <Data Id="NFe43150602261542000143550010000000761792265342">' \
                '     Hello, World!' \
                '   </Data>' \
                '</Envelope>'
 
-XML_ASSINADO = ''
 
 class test_assinatura(unittest.TestCase):
+    
+    caminho = os.path.dirname(__file__)
 
-    def test_assinar_xml(self):
-        print 'oola'
-        assinatura = Assinatura('/home/danimar/Desktop/INFOGER.pfx', '123456')
-        
-        self.assertRaises(RuntimeError, assinatura.assina_xml, XML_ASSINAR)
+    def test_assinar_xml_arquivo_invalido(self):
+        print self.caminho
+        assinatura = Assinatura(os.path.join(self.caminho, 'teste_nao_existe.pfx'), '123456')
+        self.assertRaises(Exception, assinatura.assina_xml, XML_ASSINAR)
+
+    def test_assinar_xml_senha_invalida(self):        
+        assinatura = Assinatura(os.path.join(self.caminho,'teste.pfx'), '123')
+        self.assertRaises(Exception, assinatura.assina_xml, XML_ASSINAR)
 
+    def test_assinar_xml_valido(self):        
+        assinatura = Assinatura(os.path.join(self.caminho,'teste.pfx'), '123456')
+        xml = assinatura.assina_xml(XML_ASSINAR)        
+        xml_assinado = open(os.path.join(self.caminho, 'xml_assinado.xml'), 'r').read()    
+        
+        self.assertEqual(xml_assinado, xml, 'Xml assinado é inválido')
 
-#if __name__ == "__main__":
+if __name__ == "__main__":
     #import sys;sys.argv = ['', 'Test.testName']
-#    unittest.main()
+    unittest.main()
     
\ No newline at end of file
diff --git a/pytrustnfe/test/teste.pfx b/pytrustnfe/test/teste.pfx
new file mode 100644
index 0000000..bb326ab
Binary files /dev/null and b/pytrustnfe/test/teste.pfx differ
diff --git a/pytrustnfe/test/xml_assinado.xml b/pytrustnfe/test/xml_assinado.xml
new file mode 100644
index 0000000..178375c
--- /dev/null
+++ b/pytrustnfe/test/xml_assinado.xml
@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE Envelope [
+<!ATTLIST Data Id ID #IMPLIED>
+]>
+<Envelope xmlns="urn:envelope">   <Data Id="NFe43150602261542000143550010000000761792265342">     Hello, World!   </Data><Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
+<SignedInfo>
+<CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
+<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
+<Reference URI="#NFe43150602261542000143550010000000761792265342">
+<Transforms>
+<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
+<Transform Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
+</Transforms>
+<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
+<DigestValue>Ux0WbUl0+Ck1vAlonmbcqD+iO0o=</DigestValue>
+</Reference>
+</SignedInfo>
+<SignatureValue>D7mPbktbL8eVjjlvHwHdttEBhBldotZtA6hIJ9I51PZ1Nb3KMxemEOMqbHcD4uZB
+AJ1/b0sHNst/CoOepACIwGIzUuQShYswuW9Bq84IeM4DIOu35kcaUmVAesdmPsg4
+eSBmzGHdUZYopiEO9l2iGJpPrDEDkiXtv2uN7jjKHiI=</SignatureValue>
+<KeyInfo>
+<X509Data>
+<X509Certificate>MIICMTCCAZqgAwIBAgIQfYOsIEVuAJ1FwwcTrY0t1DANBgkqhkiG9w0BAQUFADBX
+MVUwUwYDVQQDHkwAewA1ADkARgAxAEUANAA2ADEALQBEAEQARQA1AC0ANABEADIA
+RgAtAEEAMAAxAEEALQA4ADMAMwAyADIAQQA5AEUAQgA4ADMAOAB9MB4XDTE1MDYx
+NTA1NDc1N1oXDTE2MDYxNDExNDc1N1owVzFVMFMGA1UEAx5MAHsANQA5AEYAMQBF
+ADQANgAxAC0ARABEAEUANQAtADQARAAyAEYALQBBADAAMQBBAC0AOAAzADMAMgAy
+AEEAOQBFAEIAOAAzADgAfTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAk41G
+nqXXLaiOC/y0/cA4tbS+NZCqI+x4EsztgDFvPPlHstiVYcLRkni4i93gK9zoC6g0
+mh66HMVzAfE8vRNwW5b7m6nWS1SiHBon7/Mqsw4MIq3SC+J/fTbKpqwyfAuH2YZl
+AiQuQc85fyllAMLh2WrA7JgOLR/5tF3kLtpbHdECAwEAATANBgkqhkiG9w0BAQUF
+AAOBgQArdh+RyT6VxKGsXk1zhHsgwXfToe6GpTF4W8PHI1+T0WIsNForDhvst6nm
+QtgAhuZM9rxpOJuNKc+pM29EixpAiZZiRMCSWEItNyEVdUIi+YnKBcAHd88TwO86
+d126MWQ2O8cu5W1VoDp7hYBYKOnLbYi11/StO+0rzK+oPYAvIw==</X509Certificate>
+</X509Data>
+</KeyInfo>
+</Signature></Envelope>
diff --git a/requirements.txt b/requirements.txt
index 9f580cb..edacdc8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,2 @@
-nose
\ No newline at end of file
+nose
+mock
\ No newline at end of file