test(environment): improve test coverage to 100%

- Add test for unsetting previously set variables

- Add test for __exit__ with exception parameters

- Fix line length issues in random.py

- Fix Self type imports in random.py

Author: tony

src/libtmux/test/random.py

@@ -79,7 +79,8 @@ def get_test_session_name(server: Server, prefix: str = TEST_SESSION_PREFIX) ->
     'libtmux_...'
 
     Never the same twice:
-    >>> get_test_session_name(server=server) != get_test_session_name(server=server)  # pragma: no cover
+    >>> get_test_session_name(server=server) != \
+    ...     get_test_session_name(server=server)  # pragma: no cover
     True
     """
     while True:
@@ -118,7 +119,8 @@ def get_test_window_name(
 
     Never the same twice:
 
-    >>> get_test_window_name(session=session) != get_test_window_name(session=session)  # pragma: no cover
+    >>> get_test_window_name(session=session) != \
+    ...     get_test_window_name(session=session)  # pragma: no cover
     True
     """
     assert prefix is not None

tests/test/test_environment.py

@@ -3,6 +3,9 @@
 from __future__ import annotations
 
 import os
+import typing as t
+
+import pytest
 
 from libtmux.test.environment import EnvironmentVarGuard
 
@@ -81,3 +84,70 @@ def _raise_error() -> None:
     # Test cleanup after exception
     assert "TEST_NEW_VAR" not in os.environ
     assert os.environ["TEST_EXISTING_VAR"] == "original_value"
+
+
+def test_environment_var_guard_unset_and_reset() -> None:
+    """Test unsetting and then resetting a variable."""
+    env = EnvironmentVarGuard()
+
+    # Set up test variables
+    os.environ["TEST_VAR1"] = "value1"
+    os.environ["TEST_VAR2"] = "value2"
+
+    # Unset a variable
+    env.unset("TEST_VAR1")
+    assert "TEST_VAR1" not in os.environ
+
+    # Set it again with a different value
+    env.set("TEST_VAR1", "new_value1")
+    assert os.environ["TEST_VAR1"] == "new_value1"
+
+    # Unset a variable that was previously set in this context
+    env.set("TEST_VAR2", "new_value2")
+    env.unset("TEST_VAR2")
+    assert "TEST_VAR2" not in os.environ
+
+    # Cleanup
+    env.__exit__(None, None, None)
+    assert os.environ["TEST_VAR1"] == "value1"
+    assert os.environ["TEST_VAR2"] == "value2"
+
+
+def test_environment_var_guard_exit_with_exception() -> None:
+    """Test __exit__ method with exception parameters."""
+    env = EnvironmentVarGuard()
+    
+    # Set up test variables
+    os.environ["TEST_VAR"] = "original_value"
+    env.set("TEST_VAR", "new_value")
+    
+    # Call __exit__ with exception parameters
+    env.__exit__(
+        t.cast(t.Type[BaseException], RuntimeError),
+        RuntimeError("Test exception"),
+        None,
+    )
+    
+    # Verify cleanup still happened
+    assert os.environ["TEST_VAR"] == "original_value"
+
+
+def test_environment_var_guard_unset_previously_set() -> None:
+    """Test unsetting a variable that was previously set in the same context."""
+    env = EnvironmentVarGuard()
+    
+    # Make sure the variable doesn't exist initially
+    if "TEST_NEW_VAR" in os.environ:
+        del os.environ["TEST_NEW_VAR"]
+    
+    # Set a new variable
+    env.set("TEST_NEW_VAR", "new_value")
+    assert "TEST_NEW_VAR" in os.environ
+    assert os.environ["TEST_NEW_VAR"] == "new_value"
+    
+    # Now unset it - this should hit line 57
+    env.unset("TEST_NEW_VAR")
+    assert "TEST_NEW_VAR" not in os.environ
+    
+    # No need to check after cleanup since the variable was never in the environment
+    # before we started