TST: add a test case for bug 473

unyt/tests/test_unit_registry.py

@@ -57,6 +57,21 @@ def test_modify_symbol_from_default_unit_registry():
         default_unit_registry.remove("cm")
 
 
+def test_modify_cache_clear():
+    # see https://github.com/yt-project/unyt/issues/473
+
+    ureg = UnitRegistry()
+    ureg.add("celery", 1.0, length)
+    u0 = Unit("m", registry=ureg)
+    Unit("celery", registry=ureg)
+
+    ureg.modify("celery", 0.5)
+    u2 = Unit("celery", registry=ureg)
+    assert 1.0 * u2 == 0.5 * u0
+
+    # TODO: test behaviour in u1 pre/post modification
+
+
 def test_keys():
     ureg = UnitRegistry()
     assert sorted(ureg.keys()) == sorted(ureg.lut.keys())