diff --git a/tests/conftest.py b/tests/conftest.py
index b9f794c19ed..a4a0804aaa8 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -23,6 +23,7 @@
 
 from cylc.flow.cfgspec.glbl_cfg import glbl_cfg
 from cylc.flow.cfgspec.globalcfg import SPEC
+from cylc.flow.graphnode import GraphNodeParser
 from cylc.flow.parsec.config import ParsecConfig
 from cylc.flow.parsec.validate import cylc_config_validate
 from cylc.flow import flags
@@ -33,6 +34,8 @@ def test_reset():
     """Reset global state before all tests."""
     flags.verbosity = 0
     flags.cylc7_back_compat = False
+    # Reset graph node parser singleton:
+    GraphNodeParser.get_inst().clear()
 
 
 @pytest.fixture(scope='module')