Make sure InvalidVarException.fail is reset

pytest_django/plugin.py

@@ -628,18 +628,30 @@
             else:
                 return msg
 
+    # TODO: use pytest.MonkeyPatch once pytest<6.2 is not supported anymore
+    NOT_SET = object()
+    changed = False
+    previous_value = NOT_SET
     if (
         os.environ.get(INVALID_TEMPLATE_VARS_ENV, "false") == "true"
         and django_settings_is_configured()
     ):
         from django.conf import settings as dj_settings
 
         if dj_settings.TEMPLATES:
+            previous_value = dj_settings.TEMPLATES[0]["OPTIONS"].get("string_if_invalid", NOT_SET)
             dj_settings.TEMPLATES[0]["OPTIONS"]["string_if_invalid"] = InvalidVarException()
+            changed = True
+    yield
+    if changed:
+        if previous_value is NOT_SET:
+            del dj_settings.TEMPLATES[0]["OPTIONS"]["string_if_invalid"]
+        else:
+            dj_settings.TEMPLATES[0]["OPTIONS"]["string_if_invalid"] = previous_value
 
 
 @pytest.fixture(autouse=True)
-def _template_string_if_invalid_marker(request) -> None:
+def _template_string_if_invalid_marker(monkeypatch, request) -> None:
     """Apply the @pytest.mark.ignore_template_errors marker,
      internal to pytest-django."""
     marker = request.keywords.get("ignore_template_errors", None)
@@ -648,7 +660,11 @@
             from django.conf import settings as dj_settings
 
             if dj_settings.TEMPLATES:
-                dj_settings.TEMPLATES[0]["OPTIONS"]["string_if_invalid"].fail = False
+                monkeypatch.setattr(
+                    dj_settings.TEMPLATES[0]["OPTIONS"]["string_if_invalid"],
+                    "fail",
+                    False,
+                )
 
 
 @pytest.fixture(autouse=True, scope="function")

tests/test_environment.py

@@ -101,6 +101,47 @@ def test_ignore(client):
     )
 
 
+@pytest.mark.django_project(
+    extra_settings="""
+    TEMPLATE_LOADERS = (
+        'django.template.loaders.filesystem.Loader',
+        'django.template.loaders.app_directories.Loader',
+    )
+    """
+)
+def test_invalid_template_variable_marker_cleanup(django_testdir) -> None:
+    django_testdir.create_app_file(
+        "<div>{{ invalid_var }}</div>", "templates/invalid_template_base.html"
+    )
+    django_testdir.create_app_file(
+        "{% include 'invalid_template_base.html' %}", "templates/invalid_template.html"
+    )
+    django_testdir.create_test_module(
+        """
+        from django.template.loader import render_to_string
+
+        import pytest
+
+        @pytest.mark.ignore_template_errors
+        def test_ignore(client):
+            render_to_string('invalid_template.html')
+
+        def test_for_invalid_template(client):
+            render_to_string('invalid_template.html')
+
+        """
+    )
+    result = django_testdir.runpytest_subprocess("-s", "--fail-on-template-vars")
+
+    origin = "'*/tpkg/app/templates/invalid_template_base.html'"
+    result.stdout.fnmatch_lines_random(
+        [
+            "tpkg/test_the_test.py .F*",
+            f"E * Failed: Undefined template variable 'invalid_var' in {origin}",
+        ]
+    )
+
+
 @pytest.mark.django_project(
     extra_settings="""
     TEMPLATE_LOADERS = (