tests: add testing utils to set/unset env var

tests/env_var_utils.py

@@ -0,0 +1,25 @@
+import os
+from contextlib import contextmanager
+
+
+@contextmanager
+def unset_env_var(env_var: str):
+    """Context manager that unsets an environment variable, re-setting it to the original value when the context is exited."""
+    prev_value = os.environ.get(env_var, None)
+    if prev_value is not None:
+        del os.environ[env_var]
+    yield
+    if prev_value is not None:
+        os.environ[env_var] = prev_value
+
+
+@contextmanager
+def set_env_var(env_var: str, value: str):
+    """Context manager that sets an environment variable, re-setting it to the original value when the context is exited."""
+    prev_value = os.environ.get(env_var, None)
+    os.environ[env_var] = value
+    yield
+    if prev_value is not None:
+        os.environ[env_var] = prev_value
+    else:
+        del os.environ[env_var]