fix KeyError bug

Fixes #7 and adds more thorough tests.

.pre-commit-config.yaml

@@ -1,4 +1,3 @@
-fail_fast: true
 repos:
 -   repo: https://github.com/ambv/black
     rev: stable

pytailor/__version__.py

@@ -7,6 +7,6 @@
 # |__|   \/                \/
 
 
-VERSION = (0, 1, 2)
+VERSION = (0, 1, 3)
 
 __version__ = ".".join(map(str, VERSION))

pytailor/tailor.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 import os
+import warnings
 
 from .helpers import dotenv_to_dict, str_to_py
 
@@ -68,7 +69,11 @@ def from_dotenv(self, path: str):
             self.store[name] = value
 
     def watch_env_var(self, name: str):
-        """Set configuration and watch a system wideenvironment variable."""
-        value = os.environ[name]
-        mod_value = str_to_py(value)
-        self.env_store[name] = mod_value
+        """Set configuration and watch a system wide environment variable."""
+        value = os.getenv(name)
+        if not value:
+            warn_msg = f"Environment variable '{name}' not found."
+            warnings.warn(warn_msg, RuntimeWarning)
+        else:
+            mod_value = str_to_py(value)
+            self.env_store[name] = mod_value

pytest.ini

@@ -1,3 +1,5 @@
 [pytest]
 markers =
     unit
+filterwarnings =
+    ignore::RuntimeWarning

tests/test_tailor.py

@@ -11,6 +11,10 @@
 
 
 def setup_function():
+    try:
+        del os.environ["FOO"]
+    except KeyError:
+        pass
     os.environ["FOO"] = "BAR"
 
 
@@ -45,6 +49,23 @@ def test_from_object_and_then_dotenv(env_path):
     assert config["TESTING"] is False
 
 
+def test_watch_env_var_that_doesnt_exist_raises_warning():
+    config = Tailor()
+    with pytest.warns(RuntimeWarning) as warn:
+        config.watch_env_var("BAR")
+
+    assert len(warn) == 1
+    assert "not found" in warn[0].message.args[0]
+
+
+def test_watch_env_var_that_doesnt_exist_but_exists_in_config_object():
+    config = Tailor()
+    config["BAR"] = "BAZ"
+    config.watch_env_var("BAR")
+    assert "BAR" in config
+    assert config["BAR"] == "BAZ"
+
+
 def test_watch_env_var_and_change_after_watching():
     config = Tailor()
     config.watch_env_var("FOO")