diff --git a/tests/common.py b/tests/common.py
index 0ea73a3cd..5be8d0f64 100644
--- a/tests/common.py
+++ b/tests/common.py
@@ -27,6 +27,8 @@
 import inspect
 import shutil
 import tempfile
+from securesystemslib.interface import (generate_and_write_rsa_keypair,
+    generate_and_write_ed25519_keypair)
 
 import unittest
 if sys.version_info >= (3, 3):
@@ -85,6 +87,26 @@ def set_up_gpg_keys(cls):
     shutil.copytree(gpg_keys, os.path.join(os.getcwd(), cls.gnupg_home))
 
 
+class GenKeysMixin():
+  """Mixin with classmethod to create cryptographic keys in cwd. """
+  key_pw = "pw"
+
+  @classmethod
+  def set_up_keys(cls):
+    # Generated unencrypted keys
+    cls.rsa_key_path = generate_and_write_rsa_keypair()
+    cls.rsa_key_id = os.path.basename(cls.rsa_key_path)
+
+    cls.ed25519_key_path = generate_and_write_ed25519_keypair()
+    cls.ed25519_key_id = os.path.basename(cls.ed25519_key_path)
+
+    # Generate encrypted keys
+    cls.rsa_key_enc_path = generate_and_write_rsa_keypair(password=cls.key_pw)
+    cls.rsa_key_enc_id = os.path.basename(cls.rsa_key_enc_path)
+
+    cls.ed25519_key_enc_path = generate_and_write_ed25519_keypair(password=cls.key_pw)
+    cls.ed25519_key_enc_id = os.path.basename(cls.ed25519_key_enc_path)
+
 
 class CliTestCase(unittest.TestCase):
   """TestCase subclass providing a test helper that patches sys.argv with
diff --git a/tests/test_common_args.py b/tests/test_common_args.py
index 17c70fb37..c6e155b04 100644
--- a/tests/test_common_args.py
+++ b/tests/test_common_args.py
@@ -17,7 +17,32 @@
 """
 import unittest
 import argparse
-import in_toto.common_args
+from in_toto.common_args import (
+  sort_action_groups,
+  title_case_action_groups,
+  KEY_PASSWORD_ARGS,
+  KEY_PASSWORD_KWARGS,
+  parse_password_and_prompt_args)
+
+
+class TestCommonArgs(unittest.TestCase):
+  def test_parse_password_and_prompt_args(self):
+    """"Test parse -P/--password optional arg (nargs=?, const=True). """
+    parser = argparse.ArgumentParser()
+    parser.add_argument(*KEY_PASSWORD_ARGS, **KEY_PASSWORD_KWARGS)
+
+    # parameter list | expected result tuple, i.e password, prompt
+    tests = [
+      ([], (None, False)),
+      (["--password"], (None, True)),
+      (["--password", "123456"], ("123456", False)),
+      (["-P"], (None, True)),
+      (["-P", "123456"], ("123456", False))
+    ]
+
+    for idx, (params, expected) in enumerate(tests):
+      result = parse_password_and_prompt_args(parser.parse_args(params))
+      self.assertTupleEqual(result, expected, "(row {})".format(idx))
 
 
 class TestArgparseActionGroupHelpers(unittest.TestCase):
@@ -41,19 +66,18 @@ def setUp(self):
   def test_title_case_action_groups(self):
     """Test title_case_action_groups title cases action group titles. """
     # Make titles title-case (default is asserted in setUp)
-    in_toto.common_args.title_case_action_groups(self.parser)
+    title_case_action_groups(self.parser)
 
     # Assert successful title-casing
     self.assertListEqual([group.title for group in self.parser._action_groups],
         ["Positional Arguments", "Optional Arguments"])
 
 
-  def  test_sort_action_groups(self):
+  def test_sort_action_groups(self):
     """Test sort_action_groups sorts action groups by custom title order. """
     # Create custom order for titles (default is asserted in setUp)
     custom_order = ["optional arguments", "positional arguments"]
-    in_toto.common_args.sort_action_groups(
-        self.parser, title_order=custom_order)
+    sort_action_groups(self.parser, title_order=custom_order)
     # Assert successful re-ordering
     self.assertListEqual([group.title for group in self.parser._action_groups],
         custom_order)
@@ -63,10 +87,10 @@ def  test_sort_action_groups(self):
     self.parser.add_argument_group("required named arguments")
 
     # Test default custom order of action groups titles (which are title-cased)
-    in_toto.common_args.title_case_action_groups(self.parser)
-    in_toto.common_args.sort_action_groups(self.parser)
+    title_case_action_groups(self.parser)
+    sort_action_groups(self.parser)
     default_custom_order = ["Required Named Arguments", "Positional Arguments",
-    "Optional Arguments"]
+        "Optional Arguments"]
 
     # Assert successful(title-casing) re-ordering
     self.assertListEqual([group.title for group in self.parser._action_groups],