1 files changed, 101 insertions, 0 deletions
diff --git a/tests/envcontext_test.py b/tests/envcontext_test.py
new file mode 100644
index 0000000..f9d4dce
--- /dev/null
+++ b/tests/envcontext_test.py
@@ -0,0 +1,101 @@
+import os
+from unittest import mock
+
+import pytest
+
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import UNSET
+from pre_commit.envcontext import Var
+
+
+def _test(*, before, patch, expected):
+    env = before.copy()
+    with envcontext(patch, _env=env):
+        assert env == expected
+    assert env == before
+
+
+def test_trivial():
+    _test(before={}, patch={}, expected={})
+
+
+def test_noop():
+    _test(before={'foo': 'bar'}, patch=(), expected={'foo': 'bar'})
+
+
+def test_adds():
+    _test(before={}, patch=[('foo', 'bar')], expected={'foo': 'bar'})
+
+
+def test_overrides():
+    _test(
+        before={'foo': 'baz'},
+        patch=[('foo', 'bar')],
+        expected={'foo': 'bar'},
+    )
+
+
+def test_unset_but_nothing_to_unset():
+    _test(before={}, patch=[('foo', UNSET)], expected={})
+
+
+def test_unset_things_to_remove():
+    _test(
+        before={'PYTHONHOME': ''},
+        patch=[('PYTHONHOME', UNSET)],
+        expected={},
+    )
+
+
+def test_templated_environment_variable_missing():
+    _test(
+        before={},
+        patch=[('PATH', ('~/bin:', Var('PATH')))],
+        expected={'PATH': '~/bin:'},
+    )
+
+
+def test_templated_environment_variable_defaults():
+    _test(
+        before={},
+        patch=[('PATH', ('~/bin:', Var('PATH', default='/bin')))],
+        expected={'PATH': '~/bin:/bin'},
+    )
+
+
+def test_templated_environment_variable_there():
+    _test(
+        before={'PATH': '/usr/local/bin:/usr/bin'},
+        patch=[('PATH', ('~/bin:', Var('PATH')))],
+        expected={'PATH': '~/bin:/usr/local/bin:/usr/bin'},
+    )
+
+
+def test_templated_environ_sources_from_previous():
+    _test(
+        before={'foo': 'bar'},
+        patch=(
+            ('foo', 'baz'),
+            ('herp', ('foo: ', Var('foo'))),
+        ),
+        expected={'foo': 'baz', 'herp': 'foo: bar'},
+    )
+
+
+def test_exception_safety():
+    class MyError(RuntimeError):
+        pass
+
+    env = {'hello': 'world'}
+    with pytest.raises(MyError):
+        with envcontext((('foo', 'bar'),), _env=env):
+            raise MyError()
+    assert env == {'hello': 'world'}
+
+
+def test_integration_os_environ():
+    with mock.patch.dict(os.environ, {'FOO': 'bar'}, clear=True):
+        assert os.environ == {'FOO': 'bar'}
+        with envcontext((('HERP', 'derp'),)):
+            assert os.environ == {'FOO': 'bar', 'HERP': 'derp'}
+        assert os.environ == {'FOO': 'bar'}