--- a
+++ b/tests/test_preferences.py
@@ -0,0 +1,148 @@
+"""Test defaults and preferences
+Files tested: defaults.py
+"""
+
+import collections
+import os
+import unittest
+from shutil import copyfile
+
+from dosma.defaults import _Preferences
+
+import nested_lookup
+
+# Duplicate the resources file
+_test_preferences_sample_filepath = os.path.join(
+    os.path.dirname(os.path.abspath(__file__)), "resources/preferences.yml"
+)
+_test_preferences_duplicate_filepath = os.path.join(
+    os.path.dirname(os.path.abspath(__file__)), "resources/.test.preferences.yml"
+)
+
+
+class PreferencesMock(_Preferences):
+    _preferences_filepath = _test_preferences_duplicate_filepath
+
+
+class TestPreferences(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        copyfile(_test_preferences_sample_filepath, _test_preferences_duplicate_filepath)
+
+    @classmethod
+    def tearDownClass(cls):
+        if os.path.isfile(_test_preferences_duplicate_filepath):
+            os.remove(_test_preferences_duplicate_filepath)
+
+    def test_duplicate(self):
+        """Test duplicate instances share same config."""
+        a = PreferencesMock()
+        b = PreferencesMock()
+
+        assert a.config == b.config, "Configs must be the same dictionary."
+
+        # Test with _Preferences to be certain
+        a = _Preferences()
+        b = _Preferences()
+
+        assert a.config == b.config, "Configs must be the same dictionary."
+
+    def test_get(self):
+        a = PreferencesMock()
+
+        # Raise error when key doesn't exist.
+        with self.assertRaises(KeyError):
+            a.get("sample-key")
+
+        # Raise error when key is not specific.
+        assert nested_lookup.get_occurrence_of_key(a.config, "foo") > 1
+        with self.assertRaises(KeyError):
+            a.get("foo")
+
+        # No error when lookup is specific.
+        a.get("testing1/foo")
+
+    def test_set(self):
+        a = PreferencesMock()
+
+        # Raise error when key doesn't exist.
+        with self.assertRaises(KeyError):
+            a.set("sample-key", "bar")
+
+        # Raise error when key is not specific.
+        assert nested_lookup.get_occurrence_of_key(a.config, "foo") > 1, "%s." % a.config
+        with self.assertRaises(KeyError):
+            a.set("foo", 100)
+
+        # Raise error when value is not the same
+        with self.assertRaises(TypeError):
+            a.set("testing1/foo", "bar")
+
+        # Success when using full path or prefix kwarg
+        a.set("testing1/foo", 50)
+        assert a.get("testing1/foo") == 50, "Value mismatch: got %s, expected %s" % (
+            a.get("testing1/foo"),
+            50,
+        )
+
+        a.set("foo", 100, "testing1")
+        assert a.get("testing1/foo") == 100, "Value mismatch: got %s, expected %s" % (
+            a.get("testing1/foo"),
+            100,
+        )
+
+    def test_write(self):
+        a = PreferencesMock()
+
+        a.set("testing1/foo", 250)
+        a.save()
+
+        b = PreferencesMock()
+
+        assert a.config == b.config, "Configs must be the same dictionary."
+        assert a.get("testing1/foo") == b.get("testing1/foo")
+
+
+class TestPreferencesSchema(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        copyfile(_test_preferences_sample_filepath, _test_preferences_duplicate_filepath)
+
+    @classmethod
+    def tearDownClass(cls):
+        if os.path.isfile(_test_preferences_duplicate_filepath):
+            os.remove(_test_preferences_duplicate_filepath)
+
+    def test_cmd_line_schema(self):
+        """Test that the command line schema for preferences is valid.
+
+        Checks:
+            - No overlapping aliases
+            - Fields ['aliases', 'type', 'nargs', 'help'] present
+            - All aliases are list and begin with '--'
+        """
+        a = PreferencesMock()
+        config_dict = a.cmd_line_flags()
+
+        # Check to see not duplicates in aliases
+        aliases = []
+        for k in config_dict.keys():
+            aliases.extend(config_dict[k]["aliases"])
+
+        alias_duplicates = [
+            item for item, count in collections.Counter(aliases).items() if count > 1
+        ]
+        assert len(alias_duplicates) == 0, "Duplicate aliases: %s" % alias_duplicates
+
+        for k in config_dict.keys():
+            arg = config_dict[k]
+            # Check to see each field has at least 4 primary keys
+            for field in ["name", "aliases", "type", "nargs", "help"]:
+                assert field in arg.keys(), "`%s` missing from %s" % (field, k)
+
+            # Check type(aliases) is list
+            assert type(arg["aliases"]) is list, "Aliases must be list - k" % k
+
+            # Check to see each field has at least 4 primary keys
+            for alias in arg["aliases"]:
+                assert alias.startswith("--"), "Alias '%s' in %s must start with '--'" % (alias, k)