Add a simple feature test to test path uniqueness.

features/steps/path_steps.py

@@ -0,0 +1,24 @@
+from behave import given, when, then
+from peewee import IntegrityError
+from tui_rsync.models.models import create_tables
+from tui_rsync.models.models import Path
+
+@given('a path "{path_str}"')
+def given_path(context, path_str):
+    create_tables()
+    context.path_str = path_str
+
+@when('I add the path to the database')
+def add_path(context):
+    try:
+        context.path = Path.create(path=context.path_str)
+    except IntegrityError:
+        context.exception_raised = True
+    else:
+        context.exception_raised = False
+
+@then('the path should be added successfully')
+def path_has_added(context):
+    assert context.path.path == context.path_str
+    assert context.exception_raised == False
+