Add unload_dotenv() to reverse load_dotenv for tests

README.md

@@ -40,6 +40,10 @@ load_dotenv()  # reads variables from a .env file and sets them in os.environ
 
 # Code of your application, which uses environment variables (e.g. from `os.environ` or
 # `os.getenv`) as if they came from the actual environment.
+
+# In tests, unload_dotenv() removes those values from os.environ again:
+# from dotenv import unload_dotenv
+# unload_dotenv()
 ```
 
 By default, `load_dotenv()` will:

src/dotenv/__init__.py

@@ -1,6 +1,6 @@
 from typing import Any, Optional
 
-from .main import dotenv_values, find_dotenv, get_key, load_dotenv, set_key, unset_key
+from .main import dotenv_values, find_dotenv, get_key, load_dotenv, set_key, unload_dotenv, unset_key
 
 
 def load_ipython_extension(ipython: Any) -> None:
@@ -42,6 +42,7 @@ def get_cli_string(
 __all__ = [
     "get_cli_string",
     "load_dotenv",
+    "unload_dotenv",
     "dotenv_values",
     "get_key",
     "set_key",

src/dotenv/main.py

@@ -435,6 +435,35 @@ def load_dotenv(
     return dotenv.set_as_environment_variables()
 
 
+def unload_dotenv(
+    dotenv_path: Optional[StrPath] = None,
+    stream: Optional[IO[str]] = None,
+    encoding: Optional[str] = "utf-8",
+) -> bool:
+    """Remove variables defined in a `.env` file from `os.environ`.
+
+    Useful in tests so `load_dotenv()` does not leak into later cases.
+
+    A key is removed only when its current environment value still matches the
+    value from the file, so an explicit later assignment is left alone.
+
+    Returns True if at least one variable was removed.
+    """
+    values = dotenv_values(
+        dotenv_path=dotenv_path,
+        stream=stream,
+        encoding=encoding,
+    )
+    removed = False
+    for key, value in values.items():
+        if value is None:
+            continue
+        if os.environ.get(key) == value:
+            del os.environ[key]
+            removed = True
+    return removed
+
+
 def dotenv_values(
     dotenv_path: Optional[StrPath] = None,
     stream: Optional[IO[str]] = None,

tests/test_main.py

@@ -425,6 +425,36 @@ def test_load_dotenv_existing_file(dotenv_path):
     assert os.environ == {"a": "b"}
 
 
+@mock.patch.dict(os.environ, {}, clear=True)
+def test_unload_dotenv_removes_loaded_values(dotenv_path):
+    dotenv_path.write_text("a=b")
+    dotenv.load_dotenv(dotenv_path)
+
+    result = dotenv.unload_dotenv(dotenv_path)
+
+    assert result is True
+    assert "a" not in os.environ
+
+
+@mock.patch.dict(os.environ, {}, clear=True)
+def test_unload_dotenv_keeps_changed_values(dotenv_path):
+    dotenv_path.write_text("a=b")
+    dotenv.load_dotenv(dotenv_path)
+    os.environ["a"] = "later"
+
+    result = dotenv.unload_dotenv(dotenv_path)
+
+    assert result is False
+    assert os.environ["a"] == "later"
+
+
+@mock.patch.dict(os.environ, {}, clear=True)
+def test_unload_dotenv_missing_file(tmp_path):
+    result = dotenv.unload_dotenv(tmp_path / "missing.env")
+
+    assert result is False
+
+
 @pytest.mark.parametrize(
     "flag_value",
     [