Skip tests requiring certidude user

tests/test_cli.py

@@ -1,9 +1,20 @@
 import os
+import pwd
+import pytest
 from click.testing import CliRunner
 from certidude.cli import entry_point as cli
 
 runner = CliRunner()
 
+def user_check(name='certidude'):
+    try:
+        pwd.getpwnam(name)
+        return False
+    except KeyError:
+        pass
+    return True
+
+@pytest.mark.skipif(user_check(), reason="Missing certidude user")
 def test_cli():
 
     # Authority setup