Add Check class.

CHANGES.rst

@@ -0,0 +1,4 @@
+v1.0.0
+======
+
+Added ``Check`` class.

README.rst

@@ -16,3 +16,12 @@
 
 .. image:: https://img.shields.io/badge/skeleton-2023-informational
    :target: https://blog.jaraco.com/skeleton
+
+
+This library facilitates handling of environment variables.
+
+
+Check
+=====
+
+Use ``Check`` to act as a boolean gate on an environment variable.

jaraco/env.py

@@ -0,0 +1,34 @@
+import os
+
+
+class Check:
+    """
+    Check if an environment variable meets a certain expectation.
+
+    >>> setenv = getfixture('monkeypatch').setenv
+    >>> check = Check('SOME_VAR', expect='setting1')
+    >>> bool(check)
+    False
+    >>> setenv('SOME_VAR', 'setting1')
+    >>> bool(check)
+    True
+    >>> setenv('SOME_VAR', 'setting2')
+    >>> bool(check)
+    False
+
+    >>> check = Check('OTHER_VAR', expect='setting1', default='setting1')
+    >>> bool(check)
+    True
+    >>> setenv('OTHER_VAR', 'setting2')
+    >>> bool(check)
+    False
+    """
+
+    def __init__(self, key, expect, *, default=None, _lookup=os.environ):
+        self.key = key
+        self.expect = expect
+        self.default = default
+        self.lookup = _lookup
+
+    def __bool__(self):
+        return self.lookup.get(self.key, self.default) == self.expect