diff --git a/changelog/4974.doc.rst b/changelog/4974.doc.rst
new file mode 100644
index 000000000..74799c9b3
--- /dev/null
+++ b/changelog/4974.doc.rst
@@ -0,0 +1 @@
+Update docs for ``pytest_cmdline_parse`` hook to note availability liminations
diff --git a/src/_pytest/hookspec.py b/src/_pytest/hookspec.py
index 65a7f43ed..5a3eb282d 100644
--- a/src/_pytest/hookspec.py
+++ b/src/_pytest/hookspec.py
@@ -99,7 +99,8 @@ def pytest_cmdline_parse(pluginmanager, args):
     Stops at first non-None result, see :ref:`firstresult`
 
     .. note::
-        This hook will not be called for ``conftest.py`` files, only for setuptools plugins.
+        This hook will only be called for plugin classes passed to the ``plugins`` arg when using `pytest.main`_ to
+        perform an in-process test run.
 
     :param _pytest.config.PytestPluginManager pluginmanager: pytest plugin manager
     :param list[str] args: list of arguments passed on the command line
diff --git a/src/_pytest/pytester.py b/src/_pytest/pytester.py
index f8a79ebc9..7fc5eaf64 100644
--- a/src/_pytest/pytester.py
+++ b/src/_pytest/pytester.py
@@ -335,6 +335,15 @@ def testdir(request, tmpdir_factory):
     return Testdir(request, tmpdir_factory)
 
 
+@pytest.fixture
+def _config_for_test():
+    from _pytest.config import get_config
+
+    config = get_config()
+    yield config
+    config._ensure_unconfigure()  # cleanup, e.g. capman closing tmpfiles.
+
+
 rex_outcome = re.compile(r"(\d+) ([\w-]+)")
 
 
diff --git a/testing/test_config.py b/testing/test_config.py
index 07654e5ad..7e7d7afa0 100644
--- a/testing/test_config.py
+++ b/testing/test_config.py
@@ -768,10 +768,8 @@ def test_notify_exception(testdir, capfd):
     assert not err
 
 
-def test_load_initial_conftest_last_ordering(testdir):
-    from _pytest.config import get_config
-
-    pm = get_config().pluginmanager
+def test_load_initial_conftest_last_ordering(testdir, _config_for_test):
+    pm = _config_for_test.pluginmanager
 
     class My(object):
         def pytest_load_initial_conftests(self):
@@ -1043,21 +1041,17 @@ class TestOverrideIniArgs(object):
             assert rootdir == tmpdir
             assert inifile is None
 
-    def test_addopts_before_initini(self, monkeypatch):
+    def test_addopts_before_initini(self, monkeypatch, _config_for_test):
         cache_dir = ".custom_cache"
         monkeypatch.setenv("PYTEST_ADDOPTS", "-o cache_dir=%s" % cache_dir)
-        from _pytest.config import get_config
-
-        config = get_config()
+        config = _config_for_test
         config._preparse([], addopts=True)
         assert config._override_ini == ["cache_dir=%s" % cache_dir]
 
-    def test_addopts_from_env_not_concatenated(self, monkeypatch):
+    def test_addopts_from_env_not_concatenated(self, monkeypatch, _config_for_test):
         """PYTEST_ADDOPTS should not take values from normal args (#4265)."""
-        from _pytest.config import get_config
-
         monkeypatch.setenv("PYTEST_ADDOPTS", "-o")
-        config = get_config()
+        config = _config_for_test
         with pytest.raises(UsageError) as excinfo:
             config._preparse(["cache_dir=ignored"], addopts=True)
         assert (
@@ -1082,11 +1076,9 @@ class TestOverrideIniArgs(object):
         )
         assert result.ret == _pytest.main.EXIT_USAGEERROR
 
-    def test_override_ini_does_not_contain_paths(self):
+    def test_override_ini_does_not_contain_paths(self, _config_for_test):
         """Check that -o no longer swallows all options after it (#3103)"""
-        from _pytest.config import get_config
-
-        config = get_config()
+        config = _config_for_test
         config._preparse(["-o", "cache_dir=/cache", "/some/test/path"])
         assert config._override_ini == ["cache_dir=/cache"]
 
diff --git a/testing/test_pluginmanager.py b/testing/test_pluginmanager.py
index 10b54c112..614572ae4 100644
--- a/testing/test_pluginmanager.py
+++ b/testing/test_pluginmanager.py
@@ -8,7 +8,6 @@ import sys
 import types
 
 import pytest
-from _pytest.config import get_config
 from _pytest.config import PytestPluginManager
 from _pytest.main import EXIT_NOTESTSCOLLECTED
 from _pytest.main import Session
@@ -20,7 +19,7 @@ def pytestpm():
 
 
 class TestPytestPluginInteractions(object):
-    def test_addhooks_conftestplugin(self, testdir):
+    def test_addhooks_conftestplugin(self, testdir, _config_for_test):
         testdir.makepyfile(
             newhooks="""
             def pytest_myhook(xyz):
@@ -36,7 +35,7 @@ class TestPytestPluginInteractions(object):
                 return xyz + 1
         """
         )
-        config = get_config()
+        config = _config_for_test
         pm = config.pluginmanager
         pm.hook.pytest_addhooks.call_historic(
             kwargs=dict(pluginmanager=config.pluginmanager)
@@ -91,8 +90,8 @@ class TestPytestPluginInteractions(object):
         config.pluginmanager.register(A())
         assert len(values) == 2
 
-    def test_hook_tracing(self):
-        pytestpm = get_config().pluginmanager  # fully initialized with plugins
+    def test_hook_tracing(self, _config_for_test):
+        pytestpm = _config_for_test.pluginmanager  # fully initialized with plugins
         saveindent = []
 
         class api1(object):
@@ -201,8 +200,8 @@ class TestPytestPluginManager(object):
         assert pytestpm.get_plugin("pytest_p1").__name__ == "pytest_p1"
         assert pytestpm.get_plugin("pytest_p2").__name__ == "pytest_p2"
 
-    def test_consider_module_import_module(self, testdir):
-        pytestpm = get_config().pluginmanager
+    def test_consider_module_import_module(self, testdir, _config_for_test):
+        pytestpm = _config_for_test.pluginmanager
         mod = types.ModuleType("x")
         mod.pytest_plugins = "pytest_a"
         aplugin = testdir.makepyfile(pytest_a="#")