diff --git a/manifest/tests/test_utils.py b/manifest/tests/test_utils.py
new file mode 100644
index 0000000..aa51292
--- /dev/null
+++ b/manifest/tests/test_utils.py
@@ -0,0 +1,26 @@
+import pytest
+
+from ..utils import is_blacklisted
+
+
+@pytest.mark.parametrize("url", [
+    "/foo",
+    "/tools/foo",
+    "/resources/foo",
+    "/common/foo",
+    "/conformance-checkers/foo",
+    "/_certs/foo"
+])
+def test_is_blacklisted(url):
+    assert is_blacklisted(url) is True
+
+
+@pytest.mark.parametrize("url", [
+    "/foo/tools/bar",
+    "/foo/resources/bar",
+    "/foo/common/bar",
+    "/foo/conformance-checkers/bar",
+    "/foo/_certs/bar"
+])
+def test_not_is_blacklisted(url):
+    assert is_blacklisted(url) is False
diff --git a/manifest/utils.py b/manifest/utils.py
index a96ba59..9fd3b3b 100644
--- a/manifest/utils.py
+++ b/manifest/utils.py
@@ -1,7 +1,7 @@
 import os
 from six import BytesIO
 
-blacklist = ["/tools/", "/resources/", "/common/", "/conformance-checkers/", "_certs"]
+blacklist = ["/tools/", "/resources/", "/common/", "/conformance-checkers/", "/_certs/"]
 
 def rel_path_to_url(rel_path, url_base="/"):
     assert not os.path.isabs(rel_path)