forgot to add the test

test/test_clear_gate_cache.py

@@ -0,0 +1,22 @@
+from pyqcs import H, S, clear_builtin_gate_cache
+from pyqcs.gates.builtins import _H, _S
+
+
+def test_cache_is_active():
+    gates_S = [S(i) for i in range(10)]
+    gates_H = [H(i) for i in range(20)]
+
+    for s in gates_S:
+        assert s in _S._registry.values()
+
+    for h in gates_H:
+        assert h in _H._registry.values()
+
+def test_clear_cache():
+    gates_S = [S(i) for i in range(10)]
+    gates_H = [H(i) for i in range(20)]
+
+    clear_builtin_gate_cache()
+
+    assert _S._registry == {}
+    assert _H._registry == {}