diff --git a/Tests/ldif/subschema-ipa.demo1.freeipa.org.ldif b/Tests/data/subschema-ipa.demo1.freeipa.org.ldif
similarity index 100%
rename from Tests/ldif/subschema-ipa.demo1.freeipa.org.ldif
rename to Tests/data/subschema-ipa.demo1.freeipa.org.ldif
diff --git a/Tests/ldif/subschema-openldap-all.ldif b/Tests/data/subschema-openldap-all.ldif
similarity index 100%
rename from Tests/ldif/subschema-openldap-all.ldif
rename to Tests/data/subschema-openldap-all.ldif
diff --git a/Tests/t_ldap_schema_subentry.py b/Tests/t_ldap_schema_subentry.py
index 83ed006..ee79072 100644
--- a/Tests/t_ldap_schema_subentry.py
+++ b/Tests/t_ldap_schema_subentry.py
@@ -5,6 +5,7 @@
 See https://www.python-ldap.org/ for details.
 """
 
+import os
 import unittest
 import time
 
@@ -12,9 +13,11 @@
 import ldap.schema
 from ldap.schema.models import ObjectClass
 
+HERE = os.path.abspath(os.path.dirname(__file__))
+
 TEST_SUBSCHEMA_FILES = (
-    'Tests/ldif/subschema-ipa.demo1.freeipa.org.ldif',
-    'Tests/ldif/subschema-openldap-all.ldif',
+    os.path.join(HERE, 'data', 'subschema-ipa.demo1.freeipa.org.ldif'),
+    os.path.join(HERE, 'data', 'subschema-openldap-all.ldif'),
 )
 
 class TestSubschemaLDIF(unittest.TestCase):
@@ -25,9 +28,9 @@ class TestSubschemaLDIF(unittest.TestCase):
     def test_subschema_file(self):
         for test_file in TEST_SUBSCHEMA_FILES:
             # Read and parse LDIF file
-            ldif_file = open(test_file, 'rb')
-            ldif_parser = ldif.LDIFRecordList(ldif_file,max_entries=1)
-            ldif_parser.parse()
+            with open(test_file, 'rb') as ldif_file:
+                ldif_parser = ldif.LDIFRecordList(ldif_file,max_entries=1)
+                ldif_parser.parse()
             _, subschema_subentry = ldif_parser.all_records[0]
             sub_schema = ldap.schema.SubSchema(subschema_subentry)
 
diff --git a/tox.ini b/tox.ini
index b2d435c..22ca4a8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,8 +9,20 @@ envlist = py27,py33,py34,py35,py36,coverage-report
 
 [testenv]
 deps = coverage
-commands = {envpython} -m coverage run --parallel setup.py test
 passenv = WITH_GCOV
+# - Enable BytesWarning 
+# - Turn all warnings into exceptions.
+# - 'ignore:the imp module is deprecated' is required to ignore import of
+#   'imp' in distutils. Python 3.3 and 3.4 use PendingDeprecationWarning.
+commands = {envpython} -bb -Werror \
+    "-Wignore:the imp module is deprecated:DeprecationWarning" \
+    "-Wignore:the imp module is deprecated:PendingDeprecationWarning" \
+    -m coverage run --parallel setup.py test
+
+[testenv:py27]
+# No warnings with Python 2.7
+commands = {envpython} \
+    -m coverage run --parallel setup.py test
 
 [testenv:coverage-report]
 deps = coverage