Fix test polluted by env vars (#5796)

tests/unit/test_remote.py

@@ -15,8 +15,14 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Test the cylc.flow.remote module."""
 
-from cylc.flow.remote import run_cmd, construct_rsync_over_ssh_cmd, construct_ssh_cmd
+import os
 from unittest import mock
+
+import pytest
+
+from cylc.flow.remote import (
+    run_cmd, construct_rsync_over_ssh_cmd, construct_ssh_cmd
+)
 import cylc.flow
 
 
@@ -90,26 +96,29 @@ def test_construct_rsync_over_ssh_cmd():
     ]
 
 
-def test_construct_ssh_cmd_forward_env():
+def test_construct_ssh_cmd_forward_env(monkeypatch: pytest.MonkeyPatch):
     """ Test for 'ssh forward environment variables'
     """
-    import os
+    # Clear CYLC_* env vars as these will show up in the command
+    for env_var in os.environ:
+        if env_var.startswith('CYLC'):
+            monkeypatch.delenv(env_var)
 
     host = 'example.com'
     config = {
         'ssh command': 'ssh',
         'use login shell': None,
         'cylc path': None,
         'ssh forward environment variables': ['FOO', 'BAZ'],
-        }
+    }
 
     # Variable isn't set, no change to command
     expect = ['ssh', host, 'env', f'CYLC_VERSION={cylc.flow.__version__}', 'cylc', 'play']
     cmd = construct_ssh_cmd(['play'], config, host)
     assert cmd == expect
 
     # Variable is set, appears in `env` list
-    with mock.patch.dict(os.environ, {'FOO': 'BAR'}):
-        expect = ['ssh', host, 'env', f'CYLC_VERSION={cylc.flow.__version__}', 'FOO=BAR', 'cylc', 'play']
-        cmd = construct_ssh_cmd(['play'], config, host)
-        assert cmd == expect
+    monkeypatch.setenv('FOO', 'BAR')
+    expect = ['ssh', host, 'env', f'CYLC_VERSION={cylc.flow.__version__}', 'FOO=BAR', 'cylc', 'play']
+    cmd = construct_ssh_cmd(['play'], config, host)
+    assert cmd == expect