diff --git a/tests/unit/conftest.py b/tests/unit/conftest.py
index 09dcbcd40ad..924b1295998 100644
--- a/tests/unit/conftest.py
+++ b/tests/unit/conftest.py
@@ -82,36 +82,36 @@ def _tmp_run_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
         # Or:
         cylc_run_dir = tmp_run_dir()
     """
+    cylc_run_dir = tmp_path / 'cylc-run'
+    cylc_run_dir.mkdir(exist_ok=True)
+    monkeypatch.setattr('cylc.flow.pathutil._CYLC_RUN_DIR', cylc_run_dir)
+
     def __tmp_run_dir(
         id_: Optional[str] = None,
         installed: bool = False,
         named: bool = False
     ) -> Path:
-        nonlocal tmp_path
-        nonlocal monkeypatch
-        cylc_run_dir = tmp_path / 'cylc-run'
-        cylc_run_dir.mkdir(exist_ok=True)
-        monkeypatch.setattr('cylc.flow.pathutil._CYLC_RUN_DIR', cylc_run_dir)
-        if id_:
-            run_dir = cylc_run_dir.joinpath(id_)
-            run_dir.mkdir(parents=True, exist_ok=True)
-            (run_dir / WorkflowFiles.FLOW_FILE).touch(exist_ok=True)
-            (run_dir / WorkflowFiles.Service.DIRNAME).mkdir(exist_ok=True)
-            if run_dir.name.startswith('run'):
-                unlink_runN(run_dir.parent)
-                link_runN(run_dir)
-            if installed:
-                if named:
-                    if len(Path(id_).parts) < 2:
-                        raise ValueError("Named run requires two-level id_")
-                    (run_dir.parent / WorkflowFiles.Install.DIRNAME).mkdir(
-                        exist_ok=True)
-                else:
-                    (run_dir / WorkflowFiles.Install.DIRNAME).mkdir(
-                        exist_ok=True)
-
-            return run_dir
-        return cylc_run_dir
+        if not id_:
+            return cylc_run_dir
+
+        run_dir = cylc_run_dir.joinpath(id_)
+        run_dir.mkdir(parents=True, exist_ok=True)
+        (run_dir / WorkflowFiles.FLOW_FILE).touch(exist_ok=True)
+        (run_dir / WorkflowFiles.Service.DIRNAME).mkdir(exist_ok=True)
+        if run_dir.name.startswith('run'):
+            unlink_runN(run_dir.parent)
+            link_runN(run_dir)
+        if installed:
+            if named:
+                if len(Path(id_).parts) < 2:
+                    raise ValueError("Named run requires two-level id_")
+                (run_dir.parent / WorkflowFiles.Install.DIRNAME).mkdir(
+                    exist_ok=True)
+            else:
+                (run_dir / WorkflowFiles.Install.DIRNAME).mkdir(exist_ok=True)
+
+        return run_dir
+
     return __tmp_run_dir
 
 
diff --git a/tests/unit/test_clean.py b/tests/unit/test_clean.py
index a0c0ccdda1e..2a67daf4bf4 100644
--- a/tests/unit/test_clean.py
+++ b/tests/unit/test_clean.py
@@ -182,7 +182,6 @@ def test_init_clean__no_dir(
 ) -> None:
     """Test init_clean() when the run dir doesn't exist"""
     caplog.set_level(logging.INFO, CYLC_LOG)
-    tmp_run_dir()
     mock_clean = monkeymock('cylc.flow.clean.clean')
     mock_remote_clean = monkeymock('cylc.flow.clean.remote_clean')
 
@@ -754,7 +753,6 @@ def test_clean__targeted(
     """
     # --- Setup ---
     caplog.set_level(logging.DEBUG, CYLC_LOG)
-    tmp_run_dir()
     id_ = 'foo/bar'
     run_dir: Path
     files_to_delete: List[str]
diff --git a/tests/unit/test_install.py b/tests/unit/test_install.py
index 3230eea5d87..b15ba3286f8 100644
--- a/tests/unit/test_install.py
+++ b/tests/unit/test_install.py
@@ -84,7 +84,6 @@ def test_install_workflow__max_depth(
     prevent_symlinking,
 ):
     """Test that trying to install beyond max depth fails."""
-    tmp_run_dir()
     src_dir = tmp_src_dir('bar')
     if err_expected:
         with pytest.raises(WorkflowFilesError) as exc_info:
@@ -138,7 +137,6 @@ def test_install_workflow__symlink_target_exists(
     already exists."""
     id_ = 'smeagol'
     src_dir: Path = tmp_src_dir(id_)
-    tmp_run_dir()
     sym_run = tmp_path / 'sym-run'
     sym_log = tmp_path / 'sym-log'
     mock_glbl_cfg(
@@ -544,7 +542,7 @@ def test_validate_source_dir(tmp_run_dir: Callable, tmp_src_dir: Callable):
     assert "exists in source directory" in str(exc_info.value)
 
 
-def test_install_workflow_failif_name_name(tmp_src_dir):
+def test_install_workflow_failif_name_name(tmp_src_dir, tmp_run_dir):
     """If a run_name is given validate_workflow_name is called on
     the workflow and the run name in combination.
     """
@@ -560,7 +558,7 @@ def test_install_workflow_failif_name_name(tmp_src_dir):
         install_workflow(src_dir, workflow_name='foo', run_name='bar?')
 
 
-def test_install_workflow_failif_reserved_name(tmp_src_dir):
+def test_install_workflow_failif_reserved_name(tmp_src_dir, tmp_run_dir):
     """Reserved names cause install validation failure.
 
     n.b. manually defined to avoid test dependency on workflow_files.